Merge master.kernel.org:/pub/scm/linux/kernel/git/lethal/sh-2.6

[linux-2.6] / drivers / usb / host / ehci-sched.c

/*
 * Copyright (c) 2001-2004 by David Brownell
 * Copyright (c) 2003 Michal Sojka, for high-speed iso transfers
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/* this file is part of ehci-hcd.c */

/*-------------------------------------------------------------------------*/

/*
 * EHCI scheduled transaction support:  interrupt, iso, split iso
 * These are called "periodic" transactions in the EHCI spec.
 *
 * Note that for interrupt transfers, the QH/QTD manipulation is shared
 * with the "asynchronous" transaction support (control/bulk transfers).
 * The only real difference is in how interrupt transfers are scheduled.
 *
 * For ISO, we make an "iso_stream" head to serve the same role as a QH.
 * It keeps track of every ITD (or SITD) that's linked, and holds enough
 * pre-calculated schedule data to make appending to the queue be quick.
 */

static int ehci_get_frame (struct usb_hcd *hcd);

/*-------------------------------------------------------------------------*/

/*
 * periodic_next_shadow - return "next" pointer on shadow list
 * @periodic: host pointer to qh/itd/sitd
 * @tag: hardware tag for type of this record
 */
static union ehci_shadow *
periodic_next_shadow(struct ehci_hcd *ehci, union ehci_shadow *periodic,
                __hc32 tag)
{
        switch (hc32_to_cpu(ehci, tag)) {
        case Q_TYPE_QH:
                return &periodic->qh->qh_next;
        case Q_TYPE_FSTN:
                return &periodic->fstn->fstn_next;
        case Q_TYPE_ITD:
                return &periodic->itd->itd_next;
        // case Q_TYPE_SITD:
        default:
                return &periodic->sitd->sitd_next;
        }
}

/* caller must hold ehci->lock */
static void periodic_unlink (struct ehci_hcd *ehci, unsigned frame, void *ptr)
{
        union ehci_shadow       *prev_p = &ehci->pshadow[frame];
        __hc32                  *hw_p = &ehci->periodic[frame];
        union ehci_shadow       here = *prev_p;

        /* find predecessor of "ptr"; hw and shadow lists are in sync */
        while (here.ptr && here.ptr != ptr) {
                prev_p = periodic_next_shadow(ehci, prev_p,
                                Q_NEXT_TYPE(ehci, *hw_p));
                hw_p = here.hw_next;
                here = *prev_p;
        }
        /* an interrupt entry (at list end) could have been shared */
        if (!here.ptr)
                return;

        /* update shadow and hardware lists ... the old "next" pointers
         * from ptr may still be in use, the caller updates them.
         */
        *prev_p = *periodic_next_shadow(ehci, &here,
                        Q_NEXT_TYPE(ehci, *hw_p));
        *hw_p = *here.hw_next;
}

/* how many of the uframe's 125 usecs are allocated? */
static unsigned short
periodic_usecs (struct ehci_hcd *ehci, unsigned frame, unsigned uframe)
{
        __hc32                  *hw_p = &ehci->periodic [frame];
        union ehci_shadow       *q = &ehci->pshadow [frame];
        unsigned                usecs = 0;

        while (q->ptr) {
                switch (hc32_to_cpu(ehci, Q_NEXT_TYPE(ehci, *hw_p))) {
                case Q_TYPE_QH:
                        /* is it in the S-mask? */
                        if (q->qh->hw_info2 & cpu_to_hc32(ehci, 1 << uframe))
                                usecs += q->qh->usecs;
                        /* ... or C-mask? */
                        if (q->qh->hw_info2 & cpu_to_hc32(ehci,
                                        1 << (8 + uframe)))
                                usecs += q->qh->c_usecs;
                        hw_p = &q->qh->hw_next;
                        q = &q->qh->qh_next;
                        break;
                // case Q_TYPE_FSTN:
                default:
                        /* for "save place" FSTNs, count the relevant INTR
                         * bandwidth from the previous frame
                         */
                        if (q->fstn->hw_prev != EHCI_LIST_END(ehci)) {
                                ehci_dbg (ehci, "ignoring FSTN cost ...\n");
                        }
                        hw_p = &q->fstn->hw_next;
                        q = &q->fstn->fstn_next;
                        break;
                case Q_TYPE_ITD:
                        usecs += q->itd->usecs [uframe];
                        hw_p = &q->itd->hw_next;
                        q = &q->itd->itd_next;
                        break;
                case Q_TYPE_SITD:
                        /* is it in the S-mask?  (count SPLIT, DATA) */
                        if (q->sitd->hw_uframe & cpu_to_hc32(ehci,
                                        1 << uframe)) {
                                if (q->sitd->hw_fullspeed_ep &
                                                cpu_to_hc32(ehci, 1<<31))
                                        usecs += q->sitd->stream->usecs;
                                else    /* worst case for OUT start-split */
                                        usecs += HS_USECS_ISO (188);
                        }

                        /* ... C-mask?  (count CSPLIT, DATA) */
                        if (q->sitd->hw_uframe &
                                        cpu_to_hc32(ehci, 1 << (8 + uframe))) {
                                /* worst case for IN complete-split */
                                usecs += q->sitd->stream->c_usecs;
                        }

                        hw_p = &q->sitd->hw_next;
                        q = &q->sitd->sitd_next;
                        break;
                }
        }
#ifdef  DEBUG
        if (usecs > 100)
                ehci_err (ehci, "uframe %d sched overrun: %d usecs\n",
                        frame * 8 + uframe, usecs);
#endif
        return usecs;
}

/*-------------------------------------------------------------------------*/

static int same_tt (struct usb_device *dev1, struct usb_device *dev2)
{
        if (!dev1->tt || !dev2->tt)
                return 0;
        if (dev1->tt != dev2->tt)
                return 0;
        if (dev1->tt->multi)
                return dev1->ttport == dev2->ttport;
        else
                return 1;
}

#ifdef CONFIG_USB_EHCI_TT_NEWSCHED

/* Which uframe does the low/fullspeed transfer start in?
 *
 * The parameter is the mask of ssplits in "H-frame" terms
 * and this returns the transfer start uframe in "B-frame" terms,
 * which allows both to match, e.g. a ssplit in "H-frame" uframe 0
 * will cause a transfer in "B-frame" uframe 0.  "B-frames" lag
 * "H-frames" by 1 uframe.  See the EHCI spec sec 4.5 and figure 4.7.
 */
static inline unsigned char tt_start_uframe(struct ehci_hcd *ehci, __hc32 mask)
{
        unsigned char smask = QH_SMASK & hc32_to_cpu(ehci, mask);
        if (!smask) {
                ehci_err(ehci, "invalid empty smask!\n");
                /* uframe 7 can't have bw so this will indicate failure */
                return 7;
        }
        return ffs(smask) - 1;
}

static const unsigned char
max_tt_usecs[] = { 125, 125, 125, 125, 125, 125, 30, 0 };

/* carryover low/fullspeed bandwidth that crosses uframe boundries */
static inline void carryover_tt_bandwidth(unsigned short tt_usecs[8])
{
        int i;
        for (i=0; i<7; i++) {
                if (max_tt_usecs[i] < tt_usecs[i]) {
                        tt_usecs[i+1] += tt_usecs[i] - max_tt_usecs[i];
                        tt_usecs[i] = max_tt_usecs[i];
                }
        }
}

/* How many of the tt's periodic downstream 1000 usecs are allocated?
 *
 * While this measures the bandwidth in terms of usecs/uframe,
 * the low/fullspeed bus has no notion of uframes, so any particular
 * low/fullspeed transfer can "carry over" from one uframe to the next,
 * since the TT just performs downstream transfers in sequence.
 *
 * For example two seperate 100 usec transfers can start in the same uframe,
 * and the second one would "carry over" 75 usecs into the next uframe.
 */
static void
periodic_tt_usecs (
        struct ehci_hcd *ehci,
        struct usb_device *dev,
        unsigned frame,
        unsigned short tt_usecs[8]
)
{
        __hc32                  *hw_p = &ehci->periodic [frame];
        union ehci_shadow       *q = &ehci->pshadow [frame];
        unsigned char           uf;

        memset(tt_usecs, 0, 16);

        while (q->ptr) {
                switch (hc32_to_cpu(ehci, Q_NEXT_TYPE(ehci, *hw_p))) {
                case Q_TYPE_ITD:
                        hw_p = &q->itd->hw_next;
                        q = &q->itd->itd_next;
                        continue;
                case Q_TYPE_QH:
                        if (same_tt(dev, q->qh->dev)) {
                                uf = tt_start_uframe(ehci, q->qh->hw_info2);
                                tt_usecs[uf] += q->qh->tt_usecs;
                        }
                        hw_p = &q->qh->hw_next;
                        q = &q->qh->qh_next;
                        continue;
                case Q_TYPE_SITD:
                        if (same_tt(dev, q->sitd->urb->dev)) {
                                uf = tt_start_uframe(ehci, q->sitd->hw_uframe);
                                tt_usecs[uf] += q->sitd->stream->tt_usecs;
                        }
                        hw_p = &q->sitd->hw_next;
                        q = &q->sitd->sitd_next;
                        continue;
                // case Q_TYPE_FSTN:
                default:
                        ehci_dbg(ehci, "ignoring periodic frame %d FSTN\n",
                                        frame);
                        hw_p = &q->fstn->hw_next;
                        q = &q->fstn->fstn_next;
                }
        }

        carryover_tt_bandwidth(tt_usecs);

        if (max_tt_usecs[7] < tt_usecs[7])
                ehci_err(ehci, "frame %d tt sched overrun: %d usecs\n",
                        frame, tt_usecs[7] - max_tt_usecs[7]);
}

/*
 * Return true if the device's tt's downstream bus is available for a
 * periodic transfer of the specified length (usecs), starting at the
 * specified frame/uframe.  Note that (as summarized in section 11.19
 * of the usb 2.0 spec) TTs can buffer multiple transactions for each
 * uframe.
 *
 * The uframe parameter is when the fullspeed/lowspeed transfer
 * should be executed in "B-frame" terms, which is the same as the
 * highspeed ssplit's uframe (which is in "H-frame" terms).  For example
 * a ssplit in "H-frame" 0 causes a transfer in "B-frame" 0.
 * See the EHCI spec sec 4.5 and fig 4.7.
 *
 * This checks if the full/lowspeed bus, at the specified starting uframe,
 * has the specified bandwidth available, according to rules listed
 * in USB 2.0 spec section 11.18.1 fig 11-60.
 *
 * This does not check if the transfer would exceed the max ssplit
 * limit of 16, specified in USB 2.0 spec section 11.18.4 requirement #4,
 * since proper scheduling limits ssplits to less than 16 per uframe.
 */
static int tt_available (
        struct ehci_hcd         *ehci,
        unsigned                period,
        struct usb_device       *dev,
        unsigned                frame,
        unsigned                uframe,
        u16                     usecs
)
{
        if ((period == 0) || (uframe >= 7))     /* error */
                return 0;

        for (; frame < ehci->periodic_size; frame += period) {
                unsigned short tt_usecs[8];

                periodic_tt_usecs (ehci, dev, frame, tt_usecs);

                ehci_vdbg(ehci, "tt frame %d check %d usecs start uframe %d in"
                        " schedule %d/%d/%d/%d/%d/%d/%d/%d\n",
                        frame, usecs, uframe,
                        tt_usecs[0], tt_usecs[1], tt_usecs[2], tt_usecs[3],
                        tt_usecs[4], tt_usecs[5], tt_usecs[6], tt_usecs[7]);

                if (max_tt_usecs[uframe] <= tt_usecs[uframe]) {
                        ehci_vdbg(ehci, "frame %d uframe %d fully scheduled\n",
                                frame, uframe);
                        return 0;
                }

                /* special case for isoc transfers larger than 125us:
                 * the first and each subsequent fully used uframe
                 * must be empty, so as to not illegally delay
                 * already scheduled transactions
                 */
                if (125 < usecs) {
                        int ufs = (usecs / 125) - 1;
                        int i;
                        for (i = uframe; i < (uframe + ufs) && i < 8; i++)
                                if (0 < tt_usecs[i]) {
                                        ehci_vdbg(ehci,
                                                "multi-uframe xfer can't fit "
                                                "in frame %d uframe %d\n",
                                                frame, i);
                                        return 0;
                                }
                }

                tt_usecs[uframe] += usecs;

                carryover_tt_bandwidth(tt_usecs);

                /* fail if the carryover pushed bw past the last uframe's limit */
                if (max_tt_usecs[7] < tt_usecs[7]) {
                        ehci_vdbg(ehci,
                                "tt unavailable usecs %d frame %d uframe %d\n",
                                usecs, frame, uframe);
                        return 0;
                }
        }

        return 1;
}

#else

/* return true iff the device's transaction translator is available
 * for a periodic transfer starting at the specified frame, using
 * all the uframes in the mask.
 */
static int tt_no_collision (
        struct ehci_hcd         *ehci,
        unsigned                period,
        struct usb_device       *dev,
        unsigned                frame,
        u32                     uf_mask
)
{
        if (period == 0)        /* error */
                return 0;

        /* note bandwidth wastage:  split never follows csplit
         * (different dev or endpoint) until the next uframe.
         * calling convention doesn't make that distinction.
         */
        for (; frame < ehci->periodic_size; frame += period) {
                union ehci_shadow       here;
                __hc32                  type;

                here = ehci->pshadow [frame];
                type = Q_NEXT_TYPE(ehci, ehci->periodic [frame]);
                while (here.ptr) {
                        switch (hc32_to_cpu(ehci, type)) {
                        case Q_TYPE_ITD:
                                type = Q_NEXT_TYPE(ehci, here.itd->hw_next);
                                here = here.itd->itd_next;
                                continue;
                        case Q_TYPE_QH:
                                if (same_tt (dev, here.qh->dev)) {
                                        u32             mask;

                                        mask = hc32_to_cpu(ehci,
                                                        here.qh->hw_info2);
                                        /* "knows" no gap is needed */
                                        mask |= mask >> 8;
                                        if (mask & uf_mask)
                                                break;
                                }
                                type = Q_NEXT_TYPE(ehci, here.qh->hw_next);
                                here = here.qh->qh_next;
                                continue;
                        case Q_TYPE_SITD:
                                if (same_tt (dev, here.sitd->urb->dev)) {
                                        u16             mask;

                                        mask = hc32_to_cpu(ehci, here.sitd
                                                                ->hw_uframe);
                                        /* FIXME assumes no gap for IN! */
                                        mask |= mask >> 8;
                                        if (mask & uf_mask)
                                                break;
                                }
                                type = Q_NEXT_TYPE(ehci, here.sitd->hw_next);
                                here = here.sitd->sitd_next;
                                continue;
                        // case Q_TYPE_FSTN:
                        default:
                                ehci_dbg (ehci,
                                        "periodic frame %d bogus type %d\n",
                                        frame, type);
                        }

                        /* collision or error */
                        return 0;
                }
        }

        /* no collision */
        return 1;
}

#endif /* CONFIG_USB_EHCI_TT_NEWSCHED */

/*-------------------------------------------------------------------------*/

static int enable_periodic (struct ehci_hcd *ehci)
{
        u32     cmd;
        int     status;

        /* did clearing PSE did take effect yet?
         * takes effect only at frame boundaries...
         */
        status = handshake(ehci, &ehci->regs->status, STS_PSS, 0, 9 * 125);
        if (status != 0) {
                ehci_to_hcd(ehci)->state = HC_STATE_HALT;
                return status;
        }

        cmd = ehci_readl(ehci, &ehci->regs->command) | CMD_PSE;
        ehci_writel(ehci, cmd, &ehci->regs->command);
        /* posted write ... PSS happens later */
        ehci_to_hcd(ehci)->state = HC_STATE_RUNNING;

        /* make sure ehci_work scans these */
        ehci->next_uframe = ehci_readl(ehci, &ehci->regs->frame_index)
                % (ehci->periodic_size << 3);
        return 0;
}

static int disable_periodic (struct ehci_hcd *ehci)
{
        u32     cmd;
        int     status;

        /* did setting PSE not take effect yet?
         * takes effect only at frame boundaries...
         */
        status = handshake(ehci, &ehci->regs->status, STS_PSS, STS_PSS, 9 * 125);
        if (status != 0) {
                ehci_to_hcd(ehci)->state = HC_STATE_HALT;
                return status;
        }

        cmd = ehci_readl(ehci, &ehci->regs->command) & ~CMD_PSE;
        ehci_writel(ehci, cmd, &ehci->regs->command);
        /* posted write ... */

        ehci->next_uframe = -1;
        return 0;
}

/*-------------------------------------------------------------------------*/
#ifdef CONFIG_CPU_FREQ

static int safe_to_modify_i (struct ehci_hcd *ehci, struct ehci_qh *qh)
{
        int now; /* current (frame * 8) + uframe */
        int prev_start, next_start; /* uframes from/to split start */
        int start_uframe = ffs(le32_to_cpup (&qh->hw_info2) & QH_SMASK);
        int end_uframe = fls((le32_to_cpup (&qh->hw_info2) & QH_CMASK) >> 8);
        int split_duration = end_uframe - start_uframe;

        now = readl(&ehci->regs->frame_index) % (ehci->periodic_size << 3);

        next_start = ((1024 << 3) + (qh->start << 3) + start_uframe - now)
                        % (qh->period << 3);
        prev_start = (qh->period << 3) - next_start;

        /*
         * Make sure there will be at least one uframe when qh is safe.
         */
        if ((qh->period << 3) <= (ehci->i_thresh + 2 + split_duration))
                /* never safe */
                return -EINVAL;

        /*
         * Wait 1 uframe after transaction should have started, to make
         * sure controller has time to write back overlay, so we can
         * check QTD_STS_STS to see if transaction is in progress.
         */
        if ((next_start > ehci->i_thresh) && (prev_start > 1))
                /* safe to set "i" bit if split isn't in progress */
                return (qh->hw_token & STATUS_BIT(ehci)) ? 0 : 1;
        else
                return 0;
}

/* Set inactivate bit for all the split interrupt QHs. */
static void qh_inactivate_split_intr_qhs (struct ehci_hcd *ehci)
{
        struct ehci_qh  *qh;
        int             not_done, safe;
        u32             inactivate = INACTIVATE_BIT(ehci);
        u32             active = ACTIVE_BIT(ehci);

        do {
                not_done = 0;
                list_for_each_entry(qh, &ehci->split_intr_qhs,
                                split_intr_qhs) {
                        if (qh->hw_info1 & inactivate)
                                /* already off */
                                continue;
                        /*
                         * To avoid setting "I" after the start split happens,
                         * don't set it if the QH might be cached in the
                         * controller.  Some HCs (Broadcom/ServerWorks HT1000)
                         * will stop in the middle of a split transaction when
                         * the "I" bit is set.
                         */
                        safe = safe_to_modify_i(ehci, qh);
                        if (safe == 0) {
                                not_done = 1;
                        } else if (safe > 0) {
                                qh->was_active = qh->hw_token & active;
                                qh->hw_info1 |= inactivate;
                        }
                }
        } while (not_done);
        wmb();
}

static void qh_reactivate_split_intr_qhs (struct ehci_hcd *ehci)
{
        struct ehci_qh  *qh;
        u32             token;
        int             not_done, safe;
        u32             inactivate = INACTIVATE_BIT(ehci);
        u32             active = ACTIVE_BIT(ehci);
        u32             halt = HALT_BIT(ehci);

        do {
                not_done = 0;
                list_for_each_entry(qh, &ehci->split_intr_qhs, split_intr_qhs) {
                        if (!(qh->hw_info1 & inactivate)) /* already on */
                                continue;
                        /*
                         * Don't reactivate if cached, or controller might
                         * overwrite overlay after we modify it!
                         */
                        safe = safe_to_modify_i(ehci, qh);
                        if (safe == 0) {
                                not_done = 1;
                        } else if (safe > 0) {
                                /* See EHCI 1.0 section 4.15.2.4. */
                                token = qh->hw_token;
                                qh->hw_token = (token | halt) & ~active;
                                wmb();
                                qh->hw_info1 &= ~inactivate;
                                wmb();
                                qh->hw_token = (token & ~halt) | qh->was_active;
                        }
                }
        } while (not_done);
}
#endif

/* periodic schedule slots have iso tds (normal or split) first, then a
 * sparse tree for active interrupt transfers.
 *
 * this just links in a qh; caller guarantees uframe masks are set right.
 * no FSTN support (yet; ehci 0.96+)
 */
static int qh_link_periodic (struct ehci_hcd *ehci, struct ehci_qh *qh)
{
        unsigned        i;
        unsigned        period = qh->period;

        dev_dbg (&qh->dev->dev,
                "link qh%d-%04x/%p start %d [%d/%d us]\n",
                period, hc32_to_cpup(ehci, &qh->hw_info2) & (QH_CMASK | QH_SMASK),
                qh, qh->start, qh->usecs, qh->c_usecs);

#ifdef CONFIG_CPU_FREQ
        /*
         * If low/full speed interrupt QHs are inactive (because of
         * cpufreq changing processor speeds), start QH with I flag set--
         * it will automatically be cleared when cpufreq is done.
         */
        if (ehci->cpufreq_changing)
                if (!(qh->hw_info1 & (cpu_to_le32(1 << 13))))
                        qh->hw_info1 |= INACTIVATE_BIT(ehci);
#endif

        /* high bandwidth, or otherwise every microframe */
        if (period == 0)
                period = 1;

        for (i = qh->start; i < ehci->periodic_size; i += period) {
                union ehci_shadow       *prev = &ehci->pshadow[i];
                __hc32                  *hw_p = &ehci->periodic[i];
                union ehci_shadow       here = *prev;
                __hc32                  type = 0;

                /* skip the iso nodes at list head */
                while (here.ptr) {
                        type = Q_NEXT_TYPE(ehci, *hw_p);
                        if (type == cpu_to_hc32(ehci, Q_TYPE_QH))
                                break;
                        prev = periodic_next_shadow(ehci, prev, type);
                        hw_p = &here.qh->hw_next;
                        here = *prev;
                }

                /* sorting each branch by period (slow-->fast)
                 * enables sharing interior tree nodes
                 */
                while (here.ptr && qh != here.qh) {
                        if (qh->period > here.qh->period)
                                break;
                        prev = &here.qh->qh_next;
                        hw_p = &here.qh->hw_next;
                        here = *prev;
                }
                /* link in this qh, unless some earlier pass did that */
                if (qh != here.qh) {
                        qh->qh_next = here;
                        if (here.qh)
                                qh->hw_next = *hw_p;
                        wmb ();
                        prev->qh = qh;
                        *hw_p = QH_NEXT (ehci, qh->qh_dma);
                }
        }
        qh->qh_state = QH_STATE_LINKED;
        qh_get (qh);

        /* update per-qh bandwidth for usbfs */
        ehci_to_hcd(ehci)->self.bandwidth_allocated += qh->period
                ? ((qh->usecs + qh->c_usecs) / qh->period)
                : (qh->usecs * 8);

#ifdef CONFIG_CPU_FREQ
        /* add qh to list of low/full speed interrupt QHs, if applicable */
        if (!(qh->hw_info1 & (cpu_to_le32(1 << 13)))) {
                list_add(&qh->split_intr_qhs, &ehci->split_intr_qhs);
        }
#endif
        /* maybe enable periodic schedule processing */
        if (!ehci->periodic_sched++)
                return enable_periodic (ehci);

        return 0;
}

static void qh_unlink_periodic (struct ehci_hcd *ehci, struct ehci_qh *qh)
{
        unsigned        i;
        unsigned        period;

        // FIXME:
        // IF this isn't high speed
        //   and this qh is active in the current uframe
        //   (and overlay token SplitXstate is false?)
        // THEN
        //   qh->hw_info1 |= __constant_cpu_to_hc32(1 << 7 /* "ignore" */);

#ifdef CONFIG_CPU_FREQ
        /* remove qh from list of low/full speed interrupt QHs */
        if (!(qh->hw_info1 & (cpu_to_le32(1 << 13)))) {
                list_del_init(&qh->split_intr_qhs);
        }
#endif

        /* high bandwidth, or otherwise part of every microframe */
        if ((period = qh->period) == 0)
                period = 1;

        for (i = qh->start; i < ehci->periodic_size; i += period)
                periodic_unlink (ehci, i, qh);

        /* update per-qh bandwidth for usbfs */
        ehci_to_hcd(ehci)->self.bandwidth_allocated -= qh->period
                ? ((qh->usecs + qh->c_usecs) / qh->period)
                : (qh->usecs * 8);

        dev_dbg (&qh->dev->dev,
                "unlink qh%d-%04x/%p start %d [%d/%d us]\n",
                qh->period,
                hc32_to_cpup(ehci, &qh->hw_info2) & (QH_CMASK | QH_SMASK),
                qh, qh->start, qh->usecs, qh->c_usecs);

        /* qh->qh_next still "live" to HC */
        qh->qh_state = QH_STATE_UNLINK;
        qh->qh_next.ptr = NULL;
        qh_put (qh);

        /* maybe turn off periodic schedule */
        ehci->periodic_sched--;
        if (!ehci->periodic_sched)
                (void) disable_periodic (ehci);
}

static void intr_deschedule (struct ehci_hcd *ehci, struct ehci_qh *qh)
{
        unsigned        wait;

        qh_unlink_periodic (ehci, qh);

        /* simple/paranoid:  always delay, expecting the HC needs to read
         * qh->hw_next or finish a writeback after SPLIT/CSPLIT ... and
         * expect khubd to clean up after any CSPLITs we won't issue.
         * active high speed queues may need bigger delays...
         */
        if (list_empty (&qh->qtd_list)
                        || (cpu_to_hc32(ehci, QH_CMASK)
                                        & qh->hw_info2) != 0)
                wait = 2;
        else
                wait = 55;      /* worst case: 3 * 1024 */

        udelay (wait);
        qh->qh_state = QH_STATE_IDLE;
        qh->hw_next = EHCI_LIST_END(ehci);
        wmb ();
}

/*-------------------------------------------------------------------------*/

static int check_period (
        struct ehci_hcd *ehci,
        unsigned        frame,
        unsigned        uframe,
        unsigned        period,
        unsigned        usecs
) {
        int             claimed;

        /* complete split running into next frame?
         * given FSTN support, we could sometimes check...
         */
        if (uframe >= 8)
                return 0;

        /*
         * 80% periodic == 100 usec/uframe available
         * convert "usecs we need" to "max already claimed"
         */
        usecs = 100 - usecs;

        /* we "know" 2 and 4 uframe intervals were rejected; so
         * for period 0, check _every_ microframe in the schedule.
         */
        if (unlikely (period == 0)) {
                do {
                        for (uframe = 0; uframe < 7; uframe++) {
                                claimed = periodic_usecs (ehci, frame, uframe);
                                if (claimed > usecs)
                                        return 0;
                        }
                } while ((frame += 1) < ehci->periodic_size);

        /* just check the specified uframe, at that period */
        } else {
                do {
                        claimed = periodic_usecs (ehci, frame, uframe);
                        if (claimed > usecs)
                                return 0;
                } while ((frame += period) < ehci->periodic_size);
        }

        // success!
        return 1;
}

static int check_intr_schedule (
        struct ehci_hcd         *ehci,
        unsigned                frame,
        unsigned                uframe,
        const struct ehci_qh    *qh,
        __hc32                  *c_maskp
)
{
        int             retval = -ENOSPC;
        u8              mask = 0;

        if (qh->c_usecs && uframe >= 6)         /* FSTN territory? */
                goto done;

        if (!check_period (ehci, frame, uframe, qh->period, qh->usecs))
                goto done;
        if (!qh->c_usecs) {
                retval = 0;
                *c_maskp = 0;
                goto done;
        }

#ifdef CONFIG_USB_EHCI_TT_NEWSCHED
        if (tt_available (ehci, qh->period, qh->dev, frame, uframe,
                                qh->tt_usecs)) {
                unsigned i;

                /* TODO : this may need FSTN for SSPLIT in uframe 5. */
                for (i=uframe+1; i<8 && i<uframe+4; i++)
                        if (!check_period (ehci, frame, i,
                                                qh->period, qh->c_usecs))
                                goto done;
                        else
                                mask |= 1 << i;

                retval = 0;

                *c_maskp = cpu_to_hc32(ehci, mask << 8);
        }
#else
        /* Make sure this tt's buffer is also available for CSPLITs.
         * We pessimize a bit; probably the typical full speed case
         * doesn't need the second CSPLIT.
         *
         * NOTE:  both SPLIT and CSPLIT could be checked in just
         * one smart pass...
         */
        mask = 0x03 << (uframe + qh->gap_uf);
        *c_maskp = cpu_to_hc32(ehci, mask << 8);

        mask |= 1 << uframe;
        if (tt_no_collision (ehci, qh->period, qh->dev, frame, mask)) {
                if (!check_period (ehci, frame, uframe + qh->gap_uf + 1,
                                        qh->period, qh->c_usecs))
                        goto done;
                if (!check_period (ehci, frame, uframe + qh->gap_uf,
                                        qh->period, qh->c_usecs))
                        goto done;
                retval = 0;
        }
#endif
done:
        return retval;
}

/* "first fit" scheduling policy used the first time through,
 * or when the previous schedule slot can't be re-used.
 */
static int qh_schedule(struct ehci_hcd *ehci, struct ehci_qh *qh)
{
        int             status;
        unsigned        uframe;
        __hc32          c_mask;
        unsigned        frame;          /* 0..(qh->period - 1), or NO_FRAME */

        qh_refresh(ehci, qh);
        qh->hw_next = EHCI_LIST_END(ehci);
        frame = qh->start;

        /* reuse the previous schedule slots, if we can */
        if (frame < qh->period) {
                uframe = ffs(hc32_to_cpup(ehci, &qh->hw_info2) & QH_SMASK);
                status = check_intr_schedule (ehci, frame, --uframe,
                                qh, &c_mask);
        } else {
                uframe = 0;
                c_mask = 0;
                status = -ENOSPC;
        }

        /* else scan the schedule to find a group of slots such that all
         * uframes have enough periodic bandwidth available.
         */
        if (status) {
                /* "normal" case, uframing flexible except with splits */
                if (qh->period) {
                        frame = qh->period - 1;
                        do {
                                for (uframe = 0; uframe < 8; uframe++) {
                                        status = check_intr_schedule (ehci,
                                                        frame, uframe, qh,
                                                        &c_mask);
                                        if (status == 0)
                                                break;
                                }
                        } while (status && frame--);

                /* qh->period == 0 means every uframe */
                } else {
                        frame = 0;
                        status = check_intr_schedule (ehci, 0, 0, qh, &c_mask);
                }
                if (status)
                        goto done;
                qh->start = frame;

                /* reset S-frame and (maybe) C-frame masks */
                qh->hw_info2 &= cpu_to_hc32(ehci, ~(QH_CMASK | QH_SMASK));
                qh->hw_info2 |= qh->period
                        ? cpu_to_hc32(ehci, 1 << uframe)
                        : cpu_to_hc32(ehci, QH_SMASK);
                qh->hw_info2 |= c_mask;
        } else
                ehci_dbg (ehci, "reused qh %p schedule\n", qh);

        /* stuff into the periodic schedule */
        status = qh_link_periodic (ehci, qh);
done:
        return status;
}

static int intr_submit (
        struct ehci_hcd         *ehci,
        struct usb_host_endpoint *ep,
        struct urb              *urb,
        struct list_head        *qtd_list,
        gfp_t                   mem_flags
) {
        unsigned                epnum;
        unsigned long           flags;
        struct ehci_qh          *qh;
        int                     status = 0;
        struct list_head        empty;

        /* get endpoint and transfer/schedule data */
        epnum = ep->desc.bEndpointAddress;

        spin_lock_irqsave (&ehci->lock, flags);

        if (unlikely(!test_bit(HCD_FLAG_HW_ACCESSIBLE,
                        &ehci_to_hcd(ehci)->flags))) {
                status = -ESHUTDOWN;
                goto done;
        }

        /* get qh and force any scheduling errors */
        INIT_LIST_HEAD (&empty);
        qh = qh_append_tds (ehci, urb, &empty, epnum, &ep->hcpriv);
        if (qh == NULL) {
                status = -ENOMEM;
                goto done;
        }
        if (qh->qh_state == QH_STATE_IDLE) {
                if ((status = qh_schedule (ehci, qh)) != 0)
                        goto done;
        }

        /* then queue the urb's tds to the qh */
        qh = qh_append_tds (ehci, urb, qtd_list, epnum, &ep->hcpriv);
        BUG_ON (qh == NULL);

        /* ... update usbfs periodic stats */
        ehci_to_hcd(ehci)->self.bandwidth_int_reqs++;

done:
        spin_unlock_irqrestore (&ehci->lock, flags);
        if (status)
                qtd_list_free (ehci, urb, qtd_list);

        return status;
}

/*-------------------------------------------------------------------------*/

/* ehci_iso_stream ops work with both ITD and SITD */

static struct ehci_iso_stream *
iso_stream_alloc (gfp_t mem_flags)
{
        struct ehci_iso_stream *stream;

        stream = kzalloc(sizeof *stream, mem_flags);
        if (likely (stream != NULL)) {
                INIT_LIST_HEAD(&stream->td_list);
                INIT_LIST_HEAD(&stream->free_list);
                stream->next_uframe = -1;
                stream->refcount = 1;
        }
        return stream;
}

static void
iso_stream_init (
        struct ehci_hcd         *ehci,
        struct ehci_iso_stream  *stream,
        struct usb_device       *dev,
        int                     pipe,
        unsigned                interval
)
{
        static const u8 smask_out [] = { 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f };

        u32                     buf1;
        unsigned                epnum, maxp;
        int                     is_input;
        long                    bandwidth;

        /*
         * this might be a "high bandwidth" highspeed endpoint,
         * as encoded in the ep descriptor's wMaxPacket field
         */
        epnum = usb_pipeendpoint (pipe);
        is_input = usb_pipein (pipe) ? USB_DIR_IN : 0;
        maxp = usb_maxpacket(dev, pipe, !is_input);
        if (is_input) {
                buf1 = (1 << 11);
        } else {
                buf1 = 0;
        }

        /* knows about ITD vs SITD */
        if (dev->speed == USB_SPEED_HIGH) {
                unsigned multi = hb_mult(maxp);

                stream->highspeed = 1;

                maxp = max_packet(maxp);
                buf1 |= maxp;
                maxp *= multi;

                stream->buf0 = cpu_to_hc32(ehci, (epnum << 8) | dev->devnum);
                stream->buf1 = cpu_to_hc32(ehci, buf1);
                stream->buf2 = cpu_to_hc32(ehci, multi);

                /* usbfs wants to report the average usecs per frame tied up
                 * when transfers on this endpoint are scheduled ...
                 */
                stream->usecs = HS_USECS_ISO (maxp);
                bandwidth = stream->usecs * 8;
                bandwidth /= 1 << (interval - 1);

        } else {
                u32             addr;
                int             think_time;
                int             hs_transfers;

                addr = dev->ttport << 24;
                if (!ehci_is_TDI(ehci)
                                || (dev->tt->hub !=
                                        ehci_to_hcd(ehci)->self.root_hub))
                        addr |= dev->tt->hub->devnum << 16;
                addr |= epnum << 8;
                addr |= dev->devnum;
                stream->usecs = HS_USECS_ISO (maxp);
                think_time = dev->tt ? dev->tt->think_time : 0;
                stream->tt_usecs = NS_TO_US (think_time + usb_calc_bus_time (
                                dev->speed, is_input, 1, maxp));
                hs_transfers = max (1u, (maxp + 187) / 188);
                if (is_input) {
                        u32     tmp;

                        addr |= 1 << 31;
                        stream->c_usecs = stream->usecs;
                        stream->usecs = HS_USECS_ISO (1);
                        stream->raw_mask = 1;

                        /* c-mask as specified in USB 2.0 11.18.4 3.c */
                        tmp = (1 << (hs_transfers + 2)) - 1;
                        stream->raw_mask |= tmp << (8 + 2);
                } else
                        stream->raw_mask = smask_out [hs_transfers - 1];
                bandwidth = stream->usecs + stream->c_usecs;
                bandwidth /= 1 << (interval + 2);

                /* stream->splits gets created from raw_mask later */
                stream->address = cpu_to_hc32(ehci, addr);
        }
        stream->bandwidth = bandwidth;

        stream->udev = dev;

        stream->bEndpointAddress = is_input | epnum;
        stream->interval = interval;
        stream->maxp = maxp;
}

static void
iso_stream_put(struct ehci_hcd *ehci, struct ehci_iso_stream *stream)
{
        stream->refcount--;

        /* free whenever just a dev->ep reference remains.
         * not like a QH -- no persistent state (toggle, halt)
         */
        if (stream->refcount == 1) {
                int             is_in;

                // BUG_ON (!list_empty(&stream->td_list));

                while (!list_empty (&stream->free_list)) {
                        struct list_head        *entry;

                        entry = stream->free_list.next;
                        list_del (entry);

                        /* knows about ITD vs SITD */
                        if (stream->highspeed) {
                                struct ehci_itd         *itd;

                                itd = list_entry (entry, struct ehci_itd,
                                                itd_list);
                                dma_pool_free (ehci->itd_pool, itd,
                                                itd->itd_dma);
                        } else {
                                struct ehci_sitd        *sitd;

                                sitd = list_entry (entry, struct ehci_sitd,
                                                sitd_list);
                                dma_pool_free (ehci->sitd_pool, sitd,
                                                sitd->sitd_dma);
                        }
                }

                is_in = (stream->bEndpointAddress & USB_DIR_IN) ? 0x10 : 0;
                stream->bEndpointAddress &= 0x0f;
                stream->ep->hcpriv = NULL;

                if (stream->rescheduled) {
                        ehci_info (ehci, "ep%d%s-iso rescheduled "
                                "%lu times in %lu seconds\n",
                                stream->bEndpointAddress, is_in ? "in" : "out",
                                stream->rescheduled,
                                ((jiffies - stream->start)/HZ)
                                );
                }

                kfree(stream);
        }
}

static inline struct ehci_iso_stream *
iso_stream_get (struct ehci_iso_stream *stream)
{
        if (likely (stream != NULL))
                stream->refcount++;
        return stream;
}

static struct ehci_iso_stream *
iso_stream_find (struct ehci_hcd *ehci, struct urb *urb)
{
        unsigned                epnum;
        struct ehci_iso_stream  *stream;
        struct usb_host_endpoint *ep;
        unsigned long           flags;

        epnum = usb_pipeendpoint (urb->pipe);
        if (usb_pipein(urb->pipe))
                ep = urb->dev->ep_in[epnum];
        else
                ep = urb->dev->ep_out[epnum];

        spin_lock_irqsave (&ehci->lock, flags);
        stream = ep->hcpriv;

        if (unlikely (stream == NULL)) {
                stream = iso_stream_alloc(GFP_ATOMIC);
                if (likely (stream != NULL)) {
                        /* dev->ep owns the initial refcount */
                        ep->hcpriv = stream;
                        stream->ep = ep;
                        iso_stream_init(ehci, stream, urb->dev, urb->pipe,
                                        urb->interval);
                }

        /* if dev->ep [epnum] is a QH, info1.maxpacket is nonzero */
        } else if (unlikely (stream->hw_info1 != 0)) {
                ehci_dbg (ehci, "dev %s ep%d%s, not iso??\n",
                        urb->dev->devpath, epnum,
                        usb_pipein(urb->pipe) ? "in" : "out");
                stream = NULL;
        }

        /* caller guarantees an eventual matching iso_stream_put */
        stream = iso_stream_get (stream);

        spin_unlock_irqrestore (&ehci->lock, flags);
        return stream;
}

/*-------------------------------------------------------------------------*/

/* ehci_iso_sched ops can be ITD-only or SITD-only */

static struct ehci_iso_sched *
iso_sched_alloc (unsigned packets, gfp_t mem_flags)
{
        struct ehci_iso_sched   *iso_sched;
        int                     size = sizeof *iso_sched;

        size += packets * sizeof (struct ehci_iso_packet);
        iso_sched = kzalloc(size, mem_flags);
        if (likely (iso_sched != NULL)) {
                INIT_LIST_HEAD (&iso_sched->td_list);
        }
        return iso_sched;
}

static inline void
itd_sched_init(
        struct ehci_hcd         *ehci,
        struct ehci_iso_sched   *iso_sched,
        struct ehci_iso_stream  *stream,
        struct urb              *urb
)
{
        unsigned        i;
        dma_addr_t      dma = urb->transfer_dma;

        /* how many uframes are needed for these transfers */
        iso_sched->span = urb->number_of_packets * stream->interval;

        /* figure out per-uframe itd fields that we'll need later
         * when we fit new itds into the schedule.
         */
        for (i = 0; i < urb->number_of_packets; i++) {
                struct ehci_iso_packet  *uframe = &iso_sched->packet [i];
                unsigned                length;
                dma_addr_t              buf;
                u32                     trans;

                length = urb->iso_frame_desc [i].length;
                buf = dma + urb->iso_frame_desc [i].offset;

                trans = EHCI_ISOC_ACTIVE;
                trans |= buf & 0x0fff;
                if (unlikely (((i + 1) == urb->number_of_packets))
                                && !(urb->transfer_flags & URB_NO_INTERRUPT))
                        trans |= EHCI_ITD_IOC;
                trans |= length << 16;
                uframe->transaction = cpu_to_hc32(ehci, trans);

                /* might need to cross a buffer page within a uframe */
                uframe->bufp = (buf & ~(u64)0x0fff);
                buf += length;
                if (unlikely ((uframe->bufp != (buf & ~(u64)0x0fff))))
                        uframe->cross = 1;
        }
}

static void
iso_sched_free (
        struct ehci_iso_stream  *stream,
        struct ehci_iso_sched   *iso_sched
)
{
        if (!iso_sched)
                return;
        // caller must hold ehci->lock!
        list_splice (&iso_sched->td_list, &stream->free_list);
        kfree (iso_sched);
}

static int
itd_urb_transaction (
        struct ehci_iso_stream  *stream,
        struct ehci_hcd         *ehci,
        struct urb              *urb,
        gfp_t                   mem_flags
)
{
        struct ehci_itd         *itd;
        dma_addr_t              itd_dma;
        int                     i;
        unsigned                num_itds;
        struct ehci_iso_sched   *sched;
        unsigned long           flags;

        sched = iso_sched_alloc (urb->number_of_packets, mem_flags);
        if (unlikely (sched == NULL))
                return -ENOMEM;

        itd_sched_init(ehci, sched, stream, urb);

        if (urb->interval < 8)
                num_itds = 1 + (sched->span + 7) / 8;
        else
                num_itds = urb->number_of_packets;

        /* allocate/init ITDs */
        spin_lock_irqsave (&ehci->lock, flags);
        for (i = 0; i < num_itds; i++) {

                /* free_list.next might be cache-hot ... but maybe
                 * the HC caches it too. avoid that issue for now.
                 */

                /* prefer previously-allocated itds */
                if (likely (!list_empty(&stream->free_list))) {
                        itd = list_entry (stream->free_list.prev,
                                        struct ehci_itd, itd_list);
                        list_del (&itd->itd_list);
                        itd_dma = itd->itd_dma;
                } else
                        itd = NULL;

                if (!itd) {
                        spin_unlock_irqrestore (&ehci->lock, flags);
                        itd = dma_pool_alloc (ehci->itd_pool, mem_flags,
                                        &itd_dma);
                        spin_lock_irqsave (&ehci->lock, flags);
                }

                if (unlikely (NULL == itd)) {
                        iso_sched_free (stream, sched);
                        spin_unlock_irqrestore (&ehci->lock, flags);
                        return -ENOMEM;
                }
                memset (itd, 0, sizeof *itd);
                itd->itd_dma = itd_dma;
                list_add (&itd->itd_list, &sched->td_list);
        }
        spin_unlock_irqrestore (&ehci->lock, flags);

        /* temporarily store schedule info in hcpriv */
        urb->hcpriv = sched;
        urb->error_count = 0;
        return 0;
}

/*-------------------------------------------------------------------------*/

static inline int
itd_slot_ok (
        struct ehci_hcd         *ehci,
        u32                     mod,
        u32                     uframe,
        u8                      usecs,
        u32                     period
)
{
        uframe %= period;
        do {
                /* can't commit more than 80% periodic == 100 usec */
                if (periodic_usecs (ehci, uframe >> 3, uframe & 0x7)
                                > (100 - usecs))
                        return 0;

                /* we know urb->interval is 2^N uframes */
                uframe += period;
        } while (uframe < mod);
        return 1;
}

static inline int
sitd_slot_ok (
        struct ehci_hcd         *ehci,
        u32                     mod,
        struct ehci_iso_stream  *stream,
        u32                     uframe,
        struct ehci_iso_sched   *sched,
        u32                     period_uframes
)
{
        u32                     mask, tmp;
        u32                     frame, uf;

        mask = stream->raw_mask << (uframe & 7);

        /* for IN, don't wrap CSPLIT into the next frame */
        if (mask & ~0xffff)
                return 0;

        /* this multi-pass logic is simple, but performance may
         * suffer when the schedule data isn't cached.
         */

        /* check bandwidth */
        uframe %= period_uframes;
        do {
                u32             max_used;

                frame = uframe >> 3;
                uf = uframe & 7;

#ifdef CONFIG_USB_EHCI_TT_NEWSCHED
                /* The tt's fullspeed bus bandwidth must be available.
                 * tt_available scheduling guarantees 10+% for control/bulk.
                 */
                if (!tt_available (ehci, period_uframes << 3,
                                stream->udev, frame, uf, stream->tt_usecs))
                        return 0;
#else
                /* tt must be idle for start(s), any gap, and csplit.
                 * assume scheduling slop leaves 10+% for control/bulk.
                 */
                if (!tt_no_collision (ehci, period_uframes << 3,
                                stream->udev, frame, mask))
                        return 0;
#endif

                /* check starts (OUT uses more than one) */
                max_used = 100 - stream->usecs;
                for (tmp = stream->raw_mask & 0xff; tmp; tmp >>= 1, uf++) {
                        if (periodic_usecs (ehci, frame, uf) > max_used)
                                return 0;
                }

                /* for IN, check CSPLIT */
                if (stream->c_usecs) {
                        uf = uframe & 7;
                        max_used = 100 - stream->c_usecs;
                        do {
                                tmp = 1 << uf;
                                tmp <<= 8;
                                if ((stream->raw_mask & tmp) == 0)
                                        continue;
                                if (periodic_usecs (ehci, frame, uf)
                                                > max_used)
                                        return 0;
                        } while (++uf < 8);
                }

                /* we know urb->interval is 2^N uframes */
                uframe += period_uframes;
        } while (uframe < mod);

        stream->splits = cpu_to_hc32(ehci, stream->raw_mask << (uframe & 7));
        return 1;
}

/*
 * This scheduler plans almost as far into the future as it has actual
 * periodic schedule slots.  (Affected by TUNE_FLS, which defaults to
 * "as small as possible" to be cache-friendlier.)  That limits the size
 * transfers you can stream reliably; avoid more than 64 msec per urb.
 * Also avoid queue depths of less than ehci's worst irq latency (affected
 * by the per-urb URB_NO_INTERRUPT hint, the log2_irq_thresh module parameter,
 * and other factors); or more than about 230 msec total (for portability,
 * given EHCI_TUNE_FLS and the slop).  Or, write a smarter scheduler!
 */

#define SCHEDULE_SLOP   10      /* frames */

static int
iso_stream_schedule (
        struct ehci_hcd         *ehci,
        struct urb              *urb,
        struct ehci_iso_stream  *stream
)
{
        u32                     now, start, max, period;
        int                     status;
        unsigned                mod = ehci->periodic_size << 3;
        struct ehci_iso_sched   *sched = urb->hcpriv;

        if (sched->span > (mod - 8 * SCHEDULE_SLOP)) {
                ehci_dbg (ehci, "iso request %p too long\n", urb);
                status = -EFBIG;
                goto fail;
        }

        if ((stream->depth + sched->span) > mod) {
                ehci_dbg (ehci, "request %p would overflow (%d+%d>%d)\n",
                        urb, stream->depth, sched->span, mod);
                status = -EFBIG;
                goto fail;
        }

        now = ehci_readl(ehci, &ehci->regs->frame_index) % mod;

        /* when's the last uframe this urb could start? */
        max = now + mod;

        /* typical case: reuse current schedule. stream is still active,
         * and no gaps from host falling behind (irq delays etc)
         */
        if (likely (!list_empty (&stream->td_list))) {
                start = stream->next_uframe;
                if (start < now)
                        start += mod;
                if (likely ((start + sched->span) < max))
                        goto ready;
                /* else fell behind; someday, try to reschedule */
                status = -EL2NSYNC;
                goto fail;
        }

        /* need to schedule; when's the next (u)frame we could start?
         * this is bigger than ehci->i_thresh allows; scheduling itself
         * isn't free, the slop should handle reasonably slow cpus.  it
         * can also help high bandwidth if the dma and irq loads don't
         * jump until after the queue is primed.
         */
        start = SCHEDULE_SLOP * 8 + (now & ~0x07);
        start %= mod;
        stream->next_uframe = start;

        /* NOTE:  assumes URB_ISO_ASAP, to limit complexity/bugs */

        period = urb->interval;
        if (!stream->highspeed)
                period <<= 3;

        /* find a uframe slot with enough bandwidth */
        for (; start < (stream->next_uframe + period); start++) {
                int             enough_space;

                /* check schedule: enough space? */
                if (stream->highspeed)
                        enough_space = itd_slot_ok (ehci, mod, start,
                                        stream->usecs, period);
                else {
                        if ((start % 8) >= 6)
                                continue;
                        enough_space = sitd_slot_ok (ehci, mod, stream,
                                        start, sched, period);
                }

                /* schedule it here if there's enough bandwidth */
                if (enough_space) {
                        stream->next_uframe = start % mod;
                        goto ready;
                }
        }

        /* no room in the schedule */
        ehci_dbg (ehci, "iso %ssched full %p (now %d max %d)\n",
                list_empty (&stream->td_list) ? "" : "re",
                urb, now, max);
        status = -ENOSPC;

fail:
        iso_sched_free (stream, sched);
        urb->hcpriv = NULL;
        return status;

ready:
        /* report high speed start in uframes; full speed, in frames */
        urb->start_frame = stream->next_uframe;
        if (!stream->highspeed)
                urb->start_frame >>= 3;
        return 0;
}

/*-------------------------------------------------------------------------*/

static inline void
itd_init(struct ehci_hcd *ehci, struct ehci_iso_stream *stream,
                struct ehci_itd *itd)
{
        int i;

        /* it's been recently zeroed */
        itd->hw_next = EHCI_LIST_END(ehci);
        itd->hw_bufp [0] = stream->buf0;
        itd->hw_bufp [1] = stream->buf1;
        itd->hw_bufp [2] = stream->buf2;

        for (i = 0; i < 8; i++)
                itd->index[i] = -1;

        /* All other fields are filled when scheduling */
}

static inline void
itd_patch(
        struct ehci_hcd         *ehci,
        struct ehci_itd         *itd,
        struct ehci_iso_sched   *iso_sched,
        unsigned                index,
        u16                     uframe
)
{
        struct ehci_iso_packet  *uf = &iso_sched->packet [index];
        unsigned                pg = itd->pg;

        // BUG_ON (pg == 6 && uf->cross);

        uframe &= 0x07;
        itd->index [uframe] = index;

        itd->hw_transaction[uframe] = uf->transaction;
        itd->hw_transaction[uframe] |= cpu_to_hc32(ehci, pg << 12);
        itd->hw_bufp[pg] |= cpu_to_hc32(ehci, uf->bufp & ~(u32)0);
        itd->hw_bufp_hi[pg] |= cpu_to_hc32(ehci, (u32)(uf->bufp >> 32));

        /* iso_frame_desc[].offset must be strictly increasing */
        if (unlikely (uf->cross)) {
                u64     bufp = uf->bufp + 4096;

                itd->pg = ++pg;
                itd->hw_bufp[pg] |= cpu_to_hc32(ehci, bufp & ~(u32)0);
                itd->hw_bufp_hi[pg] |= cpu_to_hc32(ehci, (u32)(bufp >> 32));
        }
}

static inline void
itd_link (struct ehci_hcd *ehci, unsigned frame, struct ehci_itd *itd)
{
        /* always prepend ITD/SITD ... only QH tree is order-sensitive */
        itd->itd_next = ehci->pshadow [frame];
        itd->hw_next = ehci->periodic [frame];
        ehci->pshadow [frame].itd = itd;
        itd->frame = frame;
        wmb ();
        ehci->periodic[frame] = cpu_to_hc32(ehci, itd->itd_dma | Q_TYPE_ITD);
}

/* fit urb's itds into the selected schedule slot; activate as needed */
static int
itd_link_urb (
        struct ehci_hcd         *ehci,
        struct urb              *urb,
        unsigned                mod,
        struct ehci_iso_stream  *stream
)
{
        int                     packet;
        unsigned                next_uframe, uframe, frame;
        struct ehci_iso_sched   *iso_sched = urb->hcpriv;
        struct ehci_itd         *itd;

        next_uframe = stream->next_uframe % mod;

        if (unlikely (list_empty(&stream->td_list))) {
                ehci_to_hcd(ehci)->self.bandwidth_allocated
                                += stream->bandwidth;
                ehci_vdbg (ehci,
                        "schedule devp %s ep%d%s-iso period %d start %d.%d\n",
                        urb->dev->devpath, stream->bEndpointAddress & 0x0f,
                        (stream->bEndpointAddress & USB_DIR_IN) ? "in" : "out",
                        urb->interval,
                        next_uframe >> 3, next_uframe & 0x7);
                stream->start = jiffies;
        }
        ehci_to_hcd(ehci)->self.bandwidth_isoc_reqs++;

        /* fill iTDs uframe by uframe */
        for (packet = 0, itd = NULL; packet < urb->number_of_packets; ) {
                if (itd == NULL) {
                        /* ASSERT:  we have all necessary itds */
                        // BUG_ON (list_empty (&iso_sched->td_list));

                        /* ASSERT:  no itds for this endpoint in this uframe */

                        itd = list_entry (iso_sched->td_list.next,
                                        struct ehci_itd, itd_list);
                        list_move_tail (&itd->itd_list, &stream->td_list);
                        itd->stream = iso_stream_get (stream);
                        itd->urb = usb_get_urb (urb);
                        itd_init (ehci, stream, itd);
                }

                uframe = next_uframe & 0x07;
                frame = next_uframe >> 3;

                itd->usecs [uframe] = stream->usecs;
                itd_patch(ehci, itd, iso_sched, packet, uframe);

                next_uframe += stream->interval;
                stream->depth += stream->interval;
                next_uframe %= mod;
                packet++;

                /* link completed itds into the schedule */
                if (((next_uframe >> 3) != frame)
                                || packet == urb->number_of_packets) {
                        itd_link (ehci, frame % ehci->periodic_size, itd);
                        itd = NULL;
                }
        }
        stream->next_uframe = next_uframe;

        /* don't need that schedule data any more */
        iso_sched_free (stream, iso_sched);
        urb->hcpriv = NULL;

        timer_action (ehci, TIMER_IO_WATCHDOG);
        if (unlikely (!ehci->periodic_sched++))
                return enable_periodic (ehci);
        return 0;
}

#define ISO_ERRS (EHCI_ISOC_BUF_ERR | EHCI_ISOC_BABBLE | EHCI_ISOC_XACTERR)

static unsigned
itd_complete (
        struct ehci_hcd *ehci,
        struct ehci_itd *itd
) {
        struct urb                              *urb = itd->urb;
        struct usb_iso_packet_descriptor        *desc;
        u32                                     t;
        unsigned                                uframe;
        int                                     urb_index = -1;
        struct ehci_iso_stream                  *stream = itd->stream;
        struct usb_device                       *dev;

        /* for each uframe with a packet */
        for (uframe = 0; uframe < 8; uframe++) {
                if (likely (itd->index[uframe] == -1))
                        continue;
                urb_index = itd->index[uframe];
                desc = &urb->iso_frame_desc [urb_index];

                t = hc32_to_cpup(ehci, &itd->hw_transaction [uframe]);
                itd->hw_transaction [uframe] = 0;
                stream->depth -= stream->interval;

                /* report transfer status */
                if (unlikely (t & ISO_ERRS)) {
                        urb->error_count++;
                        if (t & EHCI_ISOC_BUF_ERR)
                                desc->status = usb_pipein (urb->pipe)
                                        ? -ENOSR  /* hc couldn't read */
                                        : -ECOMM; /* hc couldn't write */
                        else if (t & EHCI_ISOC_BABBLE)
                                desc->status = -EOVERFLOW;
                        else /* (t & EHCI_ISOC_XACTERR) */
                                desc->status = -EPROTO;

                        /* HC need not update length with this error */
                        if (!(t & EHCI_ISOC_BABBLE))
                                desc->actual_length = EHCI_ITD_LENGTH (t);
                } else if (likely ((t & EHCI_ISOC_ACTIVE) == 0)) {
                        desc->status = 0;
                        desc->actual_length = EHCI_ITD_LENGTH (t);
                }
        }

        usb_put_urb (urb);
        itd->urb = NULL;
        itd->stream = NULL;
        list_move (&itd->itd_list, &stream->free_list);
        iso_stream_put (ehci, stream);

        /* handle completion now? */
        if (likely ((urb_index + 1) != urb->number_of_packets))
                return 0;

        /* ASSERT: it's really the last itd for this urb
        list_for_each_entry (itd, &stream->td_list, itd_list)
                BUG_ON (itd->urb == urb);
         */

        /* give urb back to the driver ... can be out-of-order */
        dev = urb->dev;
        ehci_urb_done (ehci, urb);
        urb = NULL;

        /* defer stopping schedule; completion can submit */
        ehci->periodic_sched--;
        if (unlikely (!ehci->periodic_sched))
                (void) disable_periodic (ehci);
        ehci_to_hcd(ehci)->self.bandwidth_isoc_reqs--;

        if (unlikely (list_empty (&stream->td_list))) {
                ehci_to_hcd(ehci)->self.bandwidth_allocated
                                -= stream->bandwidth;
                ehci_vdbg (ehci,
                        "deschedule devp %s ep%d%s-iso\n",
                        dev->devpath, stream->bEndpointAddress & 0x0f,
                        (stream->bEndpointAddress & USB_DIR_IN) ? "in" : "out");
        }
        iso_stream_put (ehci, stream);

        return 1;
}

/*-------------------------------------------------------------------------*/

static int itd_submit (struct ehci_hcd *ehci, struct urb *urb,
        gfp_t mem_flags)
{
        int                     status = -EINVAL;
        unsigned long           flags;
        struct ehci_iso_stream  *stream;

        /* Get iso_stream head */
        stream = iso_stream_find (ehci, urb);
        if (unlikely (stream == NULL)) {
                ehci_dbg (ehci, "can't get iso stream\n");
                return -ENOMEM;
        }
        if (unlikely (urb->interval != stream->interval)) {
                ehci_dbg (ehci, "can't change iso interval %d --> %d\n",
                        stream->interval, urb->interval);
                goto done;
        }

#ifdef EHCI_URB_TRACE
        ehci_dbg (ehci,
                "%s %s urb %p ep%d%s len %d, %d pkts %d uframes [%p]\n",
                __FUNCTION__, urb->dev->devpath, urb,
                usb_pipeendpoint (urb->pipe),
                usb_pipein (urb->pipe) ? "in" : "out",
                urb->transfer_buffer_length,
                urb->number_of_packets, urb->interval,
                stream);
#endif

        /* allocate ITDs w/o locking anything */
        status = itd_urb_transaction (stream, ehci, urb, mem_flags);
        if (unlikely (status < 0)) {
                ehci_dbg (ehci, "can't init itds\n");
                goto done;
        }

        /* schedule ... need to lock */
        spin_lock_irqsave (&ehci->lock, flags);
        if (unlikely(!test_bit(HCD_FLAG_HW_ACCESSIBLE,
                               &ehci_to_hcd(ehci)->flags)))
                status = -ESHUTDOWN;
        else
                status = iso_stream_schedule (ehci, urb, stream);
        if (likely (status == 0))
                itd_link_urb (ehci, urb, ehci->periodic_size << 3, stream);
        spin_unlock_irqrestore (&ehci->lock, flags);

done:
        if (unlikely (status < 0))
                iso_stream_put (ehci, stream);
        return status;
}

#ifdef CONFIG_USB_EHCI_SPLIT_ISO

/*-------------------------------------------------------------------------*/

/*
 * "Split ISO TDs" ... used for USB 1.1 devices going through the
 * TTs in USB 2.0 hubs.  These need microframe scheduling.
 */

static inline void
sitd_sched_init(
        struct ehci_hcd         *ehci,
        struct ehci_iso_sched   *iso_sched,
        struct ehci_iso_stream  *stream,
        struct urb              *urb
)
{
        unsigned        i;
        dma_addr_t      dma = urb->transfer_dma;

        /* how many frames are needed for these transfers */
        iso_sched->span = urb->number_of_packets * stream->interval;

        /* figure out per-frame sitd fields that we'll need later
         * when we fit new sitds into the schedule.
         */
        for (i = 0; i < urb->number_of_packets; i++) {
                struct ehci_iso_packet  *packet = &iso_sched->packet [i];
                unsigned                length;
                dma_addr_t              buf;
                u32                     trans;

                length = urb->iso_frame_desc [i].length & 0x03ff;
                buf = dma + urb->iso_frame_desc [i].offset;

                trans = SITD_STS_ACTIVE;
                if (((i + 1) == urb->number_of_packets)
                                && !(urb->transfer_flags & URB_NO_INTERRUPT))
                        trans |= SITD_IOC;
                trans |= length << 16;
                packet->transaction = cpu_to_hc32(ehci, trans);

                /* might need to cross a buffer page within a td */
                packet->bufp = buf;
                packet->buf1 = (buf + length) & ~0x0fff;
                if (packet->buf1 != (buf & ~(u64)0x0fff))
                        packet->cross = 1;

                /* OUT uses multiple start-splits */
                if (stream->bEndpointAddress & USB_DIR_IN)
                        continue;
                length = (length + 187) / 188;
                if (length > 1) /* BEGIN vs ALL */
                        length |= 1 << 3;
                packet->buf1 |= length;
        }
}

static int
sitd_urb_transaction (
        struct ehci_iso_stream  *stream,
        struct ehci_hcd         *ehci,
        struct urb              *urb,
        gfp_t                   mem_flags
)
{
        struct ehci_sitd        *sitd;
        dma_addr_t              sitd_dma;
        int                     i;
        struct ehci_iso_sched   *iso_sched;
        unsigned long           flags;

        iso_sched = iso_sched_alloc (urb->number_of_packets, mem_flags);
        if (iso_sched == NULL)
                return -ENOMEM;

        sitd_sched_init(ehci, iso_sched, stream, urb);

        /* allocate/init sITDs */
        spin_lock_irqsave (&ehci->lock, flags);
        for (i = 0; i < urb->number_of_packets; i++) {

                /* NOTE:  for now, we don't try to handle wraparound cases
                 * for IN (using sitd->hw_backpointer, like a FSTN), which
                 * means we never need two sitds for full speed packets.
                 */

                /* free_list.next might be cache-hot ... but maybe
                 * the HC caches it too. avoid that issue for now.
                 */

                /* prefer previously-allocated sitds */
                if (!list_empty(&stream->free_list)) {
                        sitd = list_entry (stream->free_list.prev,
                                         struct ehci_sitd, sitd_list);
                        list_del (&sitd->sitd_list);
                        sitd_dma = sitd->sitd_dma;
                } else
                        sitd = NULL;

                if (!sitd) {
                        spin_unlock_irqrestore (&ehci->lock, flags);
                        sitd = dma_pool_alloc (ehci->sitd_pool, mem_flags,
                                        &sitd_dma);
                        spin_lock_irqsave (&ehci->lock, flags);
                }

                if (!sitd) {
                        iso_sched_free (stream, iso_sched);
                        spin_unlock_irqrestore (&ehci->lock, flags);
                        return -ENOMEM;
                }
                memset (sitd, 0, sizeof *sitd);
                sitd->sitd_dma = sitd_dma;
                list_add (&sitd->sitd_list, &iso_sched->td_list);
        }

        /* temporarily store schedule info in hcpriv */
        urb->hcpriv = iso_sched;
        urb->error_count = 0;

        spin_unlock_irqrestore (&ehci->lock, flags);
        return 0;
}

/*-------------------------------------------------------------------------*/

static inline void
sitd_patch(
        struct ehci_hcd         *ehci,
        struct ehci_iso_stream  *stream,
        struct ehci_sitd        *sitd,
        struct ehci_iso_sched   *iso_sched,
        unsigned                index
)
{
        struct ehci_iso_packet  *uf = &iso_sched->packet [index];
        u64                     bufp = uf->bufp;

        sitd->hw_next = EHCI_LIST_END(ehci);
        sitd->hw_fullspeed_ep = stream->address;
        sitd->hw_uframe = stream->splits;
        sitd->hw_results = uf->transaction;
        sitd->hw_backpointer = EHCI_LIST_END(ehci);

        bufp = uf->bufp;
        sitd->hw_buf[0] = cpu_to_hc32(ehci, bufp);
        sitd->hw_buf_hi[0] = cpu_to_hc32(ehci, bufp >> 32);

        sitd->hw_buf[1] = cpu_to_hc32(ehci, uf->buf1);
        if (uf->cross)
                bufp += 4096;
        sitd->hw_buf_hi[1] = cpu_to_hc32(ehci, bufp >> 32);
        sitd->index = index;
}

static inline void
sitd_link (struct ehci_hcd *ehci, unsigned frame, struct ehci_sitd *sitd)
{
        /* note: sitd ordering could matter (CSPLIT then SSPLIT) */
        sitd->sitd_next = ehci->pshadow [frame];
        sitd->hw_next = ehci->periodic [frame];
        ehci->pshadow [frame].sitd = sitd;
        sitd->frame = frame;
        wmb ();
        ehci->periodic[frame] = cpu_to_hc32(ehci, sitd->sitd_dma | Q_TYPE_SITD);
}

/* fit urb's sitds into the selected schedule slot; activate as needed */
static int
sitd_link_urb (
        struct ehci_hcd         *ehci,
        struct urb              *urb,
        unsigned                mod,
        struct ehci_iso_stream  *stream
)
{
        int                     packet;
        unsigned                next_uframe;
        struct ehci_iso_sched   *sched = urb->hcpriv;
        struct ehci_sitd        *sitd;

        next_uframe = stream->next_uframe;

        if (list_empty(&stream->td_list)) {
                /* usbfs ignores TT bandwidth */
                ehci_to_hcd(ehci)->self.bandwidth_allocated
                                += stream->bandwidth;
                ehci_vdbg (ehci,
                        "sched devp %s ep%d%s-iso [%d] %dms/%04x\n",
                        urb->dev->devpath, stream->bEndpointAddress & 0x0f,
                        (stream->bEndpointAddress & USB_DIR_IN) ? "in" : "out",
                        (next_uframe >> 3) % ehci->periodic_size,
                        stream->interval, hc32_to_cpu(ehci, stream->splits));
                stream->start = jiffies;
        }
        ehci_to_hcd(ehci)->self.bandwidth_isoc_reqs++;

        /* fill sITDs frame by frame */
        for (packet = 0, sitd = NULL;
                        packet < urb->number_of_packets;
                        packet++) {

                /* ASSERT:  we have all necessary sitds */
                BUG_ON (list_empty (&sched->td_list));

                /* ASSERT:  no itds for this endpoint in this frame */

                sitd = list_entry (sched->td_list.next,
                                struct ehci_sitd, sitd_list);
                list_move_tail (&sitd->sitd_list, &stream->td_list);
                sitd->stream = iso_stream_get (stream);
                sitd->urb = usb_get_urb (urb);

                sitd_patch(ehci, stream, sitd, sched, packet);
                sitd_link (ehci, (next_uframe >> 3) % ehci->periodic_size,
                                sitd);

                next_uframe += stream->interval << 3;
                stream->depth += stream->interval << 3;
        }
        stream->next_uframe = next_uframe % mod;

        /* don't need that schedule data any more */
        iso_sched_free (stream, sched);
        urb->hcpriv = NULL;

        timer_action (ehci, TIMER_IO_WATCHDOG);
        if (!ehci->periodic_sched++)
                return enable_periodic (ehci);
        return 0;
}

/*-------------------------------------------------------------------------*/

#define SITD_ERRS (SITD_STS_ERR | SITD_STS_DBE | SITD_STS_BABBLE \
                                | SITD_STS_XACT | SITD_STS_MMF)

static unsigned
sitd_complete (
        struct ehci_hcd         *ehci,
        struct ehci_sitd        *sitd
) {
        struct urb                              *urb = sitd->urb;
        struct usb_iso_packet_descriptor        *desc;
        u32                                     t;
        int                                     urb_index = -1;
        struct ehci_iso_stream                  *stream = sitd->stream;
        struct usb_device                       *dev;

        urb_index = sitd->index;
        desc = &urb->iso_frame_desc [urb_index];
        t = hc32_to_cpup(ehci, &sitd->hw_results);

        /* report transfer status */
        if (t & SITD_ERRS) {
                urb->error_count++;
                if (t & SITD_STS_DBE)
                        desc->status = usb_pipein (urb->pipe)
                                ? -ENOSR  /* hc couldn't read */
                                : -ECOMM; /* hc couldn't write */
                else if (t & SITD_STS_BABBLE)
                        desc->status = -EOVERFLOW;
                else /* XACT, MMF, etc */
                        desc->status = -EPROTO;
        } else {
                desc->status = 0;
                desc->actual_length = desc->length - SITD_LENGTH (t);
        }

        usb_put_urb (urb);
        sitd->urb = NULL;
        sitd->stream = NULL;
        list_move (&sitd->sitd_list, &stream->free_list);
        stream->depth -= stream->interval << 3;
        iso_stream_put (ehci, stream);

        /* handle completion now? */
        if ((urb_index + 1) != urb->number_of_packets)
                return 0;

        /* ASSERT: it's really the last sitd for this urb
        list_for_each_entry (sitd, &stream->td_list, sitd_list)
                BUG_ON (sitd->urb == urb);
         */

        /* give urb back to the driver */
        dev = urb->dev;
        ehci_urb_done (ehci, urb);
        urb = NULL;

        /* defer stopping schedule; completion can submit */
        ehci->periodic_sched--;
        if (!ehci->periodic_sched)
                (void) disable_periodic (ehci);
        ehci_to_hcd(ehci)->self.bandwidth_isoc_reqs--;

        if (list_empty (&stream->td_list)) {
                ehci_to_hcd(ehci)->self.bandwidth_allocated
                                -= stream->bandwidth;
                ehci_vdbg (ehci,
                        "deschedule devp %s ep%d%s-iso\n",
                        dev->devpath, stream->bEndpointAddress & 0x0f,
                        (stream->bEndpointAddress & USB_DIR_IN) ? "in" : "out");
        }
        iso_stream_put (ehci, stream);

        return 1;
}


static int sitd_submit (struct ehci_hcd *ehci, struct urb *urb,
        gfp_t mem_flags)
{
        int                     status = -EINVAL;
        unsigned long           flags;
        struct ehci_iso_stream  *stream;

        /* Get iso_stream head */
        stream = iso_stream_find (ehci, urb);
        if (stream == NULL) {
                ehci_dbg (ehci, "can't get iso stream\n");
                return -ENOMEM;
        }
        if (urb->interval != stream->interval) {
                ehci_dbg (ehci, "can't change iso interval %d --> %d\n",
                        stream->interval, urb->interval);
                goto done;
        }

#ifdef EHCI_URB_TRACE
        ehci_dbg (ehci,
                "submit %p dev%s ep%d%s-iso len %d\n",
                urb, urb->dev->devpath,
                usb_pipeendpoint (urb->pipe),
                usb_pipein (urb->pipe) ? "in" : "out",
                urb->transfer_buffer_length);
#endif

        /* allocate SITDs */
        status = sitd_urb_transaction (stream, ehci, urb, mem_flags);
        if (status < 0) {
                ehci_dbg (ehci, "can't init sitds\n");
                goto done;
        }

        /* schedule ... need to lock */
        spin_lock_irqsave (&ehci->lock, flags);
        if (unlikely(!test_bit(HCD_FLAG_HW_ACCESSIBLE,
                               &ehci_to_hcd(ehci)->flags)))
                status = -ESHUTDOWN;
        else
                status = iso_stream_schedule (ehci, urb, stream);
        if (status == 0)
                sitd_link_urb (ehci, urb, ehci->periodic_size << 3, stream);
        spin_unlock_irqrestore (&ehci->lock, flags);

done:
        if (status < 0)
                iso_stream_put (ehci, stream);
        return status;
}

#else

static inline int
sitd_submit (struct ehci_hcd *ehci, struct urb *urb, gfp_t mem_flags)
{
        ehci_dbg (ehci, "split iso support is disabled\n");
        return -ENOSYS;
}

static inline unsigned
sitd_complete (
        struct ehci_hcd         *ehci,
        struct ehci_sitd        *sitd
) {
        ehci_err (ehci, "sitd_complete %p?\n", sitd);
        return 0;
}

#endif /* USB_EHCI_SPLIT_ISO */

/*-------------------------------------------------------------------------*/

static void
scan_periodic (struct ehci_hcd *ehci)
{
        unsigned        frame, clock, now_uframe, mod;
        unsigned        modified;

        mod = ehci->periodic_size << 3;

        /*
         * When running, scan from last scan point up to "now"
         * else clean up by scanning everything that's left.
         * Touches as few pages as possible:  cache-friendly.
         */
        now_uframe = ehci->next_uframe;
        if (HC_IS_RUNNING (ehci_to_hcd(ehci)->state))
                clock = ehci_readl(ehci, &ehci->regs->frame_index);
        else
                clock = now_uframe + mod - 1;
        clock %= mod;

        for (;;) {
                union ehci_shadow       q, *q_p;
                __hc32                  type, *hw_p;
                unsigned                uframes;

                /* don't scan past the live uframe */
                frame = now_uframe >> 3;
                if (frame == (clock >> 3))
                        uframes = now_uframe & 0x07;
                else {
                        /* safe to scan the whole frame at once */
                        now_uframe |= 0x07;
                        uframes = 8;
                }

restart:
                /* scan each element in frame's queue for completions */
                q_p = &ehci->pshadow [frame];
                hw_p = &ehci->periodic [frame];
                q.ptr = q_p->ptr;
                type = Q_NEXT_TYPE(ehci, *hw_p);
                modified = 0;

                while (q.ptr != NULL) {
                        unsigned                uf;
                        union ehci_shadow       temp;
                        int                     live;

                        live = HC_IS_RUNNING (ehci_to_hcd(ehci)->state);
                        switch (hc32_to_cpu(ehci, type)) {
                        case Q_TYPE_QH:
                                /* handle any completions */
                                temp.qh = qh_get (q.qh);
                                type = Q_NEXT_TYPE(ehci, q.qh->hw_next);
                                q = q.qh->qh_next;
                                modified = qh_completions (ehci, temp.qh);
                                if (unlikely (list_empty (&temp.qh->qtd_list)))
                                        intr_deschedule (ehci, temp.qh);
                                qh_put (temp.qh);
                                break;
                        case Q_TYPE_FSTN:
                                /* for "save place" FSTNs, look at QH entries
                                 * in the previous frame for completions.
                                 */
                                if (q.fstn->hw_prev != EHCI_LIST_END(ehci)) {
                                        dbg ("ignoring completions from FSTNs");
                                }
                                type = Q_NEXT_TYPE(ehci, q.fstn->hw_next);
                                q = q.fstn->fstn_next;
                                break;
                        case Q_TYPE_ITD:
                                /* skip itds for later in the frame */
                                rmb ();
                                for (uf = live ? uframes : 8; uf < 8; uf++) {
                                        if (0 == (q.itd->hw_transaction [uf]
                                                        & ITD_ACTIVE(ehci)))
                                                continue;
                                        q_p = &q.itd->itd_next;
                                        hw_p = &q.itd->hw_next;
                                        type = Q_NEXT_TYPE(ehci,
                                                        q.itd->hw_next);
                                        q = *q_p;
                                        break;
                                }
                                if (uf != 8)
                                        break;

                                /* this one's ready ... HC won't cache the
                                 * pointer for much longer, if at all.
                                 */
                                *q_p = q.itd->itd_next;
                                *hw_p = q.itd->hw_next;
                                type = Q_NEXT_TYPE(ehci, q.itd->hw_next);
                                wmb();
                                modified = itd_complete (ehci, q.itd);
                                q = *q_p;
                                break;
                        case Q_TYPE_SITD:
                                if ((q.sitd->hw_results & SITD_ACTIVE(ehci))
                                                && live) {
                                        q_p = &q.sitd->sitd_next;
                                        hw_p = &q.sitd->hw_next;
                                        type = Q_NEXT_TYPE(ehci,
                                                        q.sitd->hw_next);
                                        q = *q_p;
                                        break;
                                }
                                *q_p = q.sitd->sitd_next;
                                *hw_p = q.sitd->hw_next;
                                type = Q_NEXT_TYPE(ehci, q.sitd->hw_next);
                                wmb();
                                modified = sitd_complete (ehci, q.sitd);
                                q = *q_p;
                                break;
                        default:
                                dbg ("corrupt type %d frame %d shadow %p",
                                        type, frame, q.ptr);
                                // BUG ();
                                q.ptr = NULL;
                        }

                        /* assume completion callbacks modify the queue */
                        if (unlikely (modified))
                                goto restart;
                }

                /* stop when we catch up to the HC */

                // FIXME:  this assumes we won't get lapped when
                // latencies climb; that should be rare, but...
                // detect it, and just go all the way around.
                // FLR might help detect this case, so long as latencies
                // don't exceed periodic_size msec (default 1.024 sec).

                // FIXME:  likewise assumes HC doesn't halt mid-scan

                if (now_uframe == clock) {
                        unsigned        now;

                        if (!HC_IS_RUNNING (ehci_to_hcd(ehci)->state))
                                break;
                        ehci->next_uframe = now_uframe;
                        now = ehci_readl(ehci, &ehci->regs->frame_index) % mod;
                        if (now_uframe == now)
                                break;

                        /* rescan the rest of this frame, then ... */
                        clock = now;
                } else {
                        now_uframe++;
                        now_uframe %= mod;
                }
        }
}