Merge branch 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[linux-2.6] / drivers / mmc / host / mmc_spi.c

/*
 * mmc_spi.c - Access SD/MMC cards through SPI master controllers
 *
 * (C) Copyright 2005, Intec Automation,
 *              Mike Lavender (mike@steroidmicros)
 * (C) Copyright 2006-2007, David Brownell
 * (C) Copyright 2007, Axis Communications,
 *              Hans-Peter Nilsson (hp@axis.com)
 * (C) Copyright 2007, ATRON electronic GmbH,
 *              Jan Nikitenko <jan.nikitenko@gmail.com>
 *
 *
 * 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.
 */
#include <linux/hrtimer.h>
#include <linux/delay.h>
#include <linux/bio.h>
#include <linux/dma-mapping.h>
#include <linux/crc7.h>
#include <linux/crc-itu-t.h>
#include <linux/scatterlist.h>

#include <linux/mmc/host.h>
#include <linux/mmc/mmc.h>              /* for R1_SPI_* bit values */

#include <linux/spi/spi.h>
#include <linux/spi/mmc_spi.h>

#include <asm/unaligned.h>


/* NOTES:
 *
 * - For now, we won't try to interoperate with a real mmc/sd/sdio
 *   controller, although some of them do have hardware support for
 *   SPI protocol.  The main reason for such configs would be mmc-ish
 *   cards like DataFlash, which don't support that "native" protocol.
 *
 *   We don't have a "DataFlash/MMC/SD/SDIO card slot" abstraction to
 *   switch between driver stacks, and in any case if "native" mode
 *   is available, it will be faster and hence preferable.
 *
 * - MMC depends on a different chipselect management policy than the
 *   SPI interface currently supports for shared bus segments:  it needs
 *   to issue multiple spi_message requests with the chipselect active,
 *   using the results of one message to decide the next one to issue.
 *
 *   Pending updates to the programming interface, this driver expects
 *   that it not share the bus with other drivers (precluding conflicts).
 *
 * - We tell the controller to keep the chipselect active from the
 *   beginning of an mmc_host_ops.request until the end.  So beware
 *   of SPI controller drivers that mis-handle the cs_change flag!
 *
 *   However, many cards seem OK with chipselect flapping up/down
 *   during that time ... at least on unshared bus segments.
 */


/*
 * Local protocol constants, internal to data block protocols.
 */

/* Response tokens used to ack each block written: */
#define SPI_MMC_RESPONSE_CODE(x)        ((x) & 0x1f)
#define SPI_RESPONSE_ACCEPTED           ((2 << 1)|1)
#define SPI_RESPONSE_CRC_ERR            ((5 << 1)|1)
#define SPI_RESPONSE_WRITE_ERR          ((6 << 1)|1)

/* Read and write blocks start with these tokens and end with crc;
 * on error, read tokens act like a subset of R2_SPI_* values.
 */
#define SPI_TOKEN_SINGLE        0xfe    /* single block r/w, multiblock read */
#define SPI_TOKEN_MULTI_WRITE   0xfc    /* multiblock write */
#define SPI_TOKEN_STOP_TRAN     0xfd    /* terminate multiblock write */

#define MMC_SPI_BLOCKSIZE       512


/* These fixed timeouts come from the latest SD specs, which say to ignore
 * the CSD values.  The R1B value is for card erase (e.g. the "I forgot the
 * card's password" scenario); it's mostly applied to STOP_TRANSMISSION after
 * reads which takes nowhere near that long.  Older cards may be able to use
 * shorter timeouts ... but why bother?
 */
#define r1b_timeout             ktime_set(3, 0)


/****************************************************************************/

/*
 * Local Data Structures
 */

/* "scratch" is per-{command,block} data exchanged with the card */
struct scratch {
        u8                      status[29];
        u8                      data_token;
        __be16                  crc_val;
};

struct mmc_spi_host {
        struct mmc_host         *mmc;
        struct spi_device       *spi;

        unsigned char           power_mode;
        u16                     powerup_msecs;

        struct mmc_spi_platform_data    *pdata;

        /* for bulk data transfers */
        struct spi_transfer     token, t, crc, early_status;
        struct spi_message      m;

        /* for status readback */
        struct spi_transfer     status;
        struct spi_message      readback;

        /* underlying DMA-aware controller, or null */
        struct device           *dma_dev;

        /* buffer used for commands and for message "overhead" */
        struct scratch          *data;
        dma_addr_t              data_dma;

        /* Specs say to write ones most of the time, even when the card
         * has no need to read its input data; and many cards won't care.
         * This is our source of those ones.
         */
        void                    *ones;
        dma_addr_t              ones_dma;
};


/****************************************************************************/

/*
 * MMC-over-SPI protocol glue, used by the MMC stack interface
 */

static inline int mmc_cs_off(struct mmc_spi_host *host)
{
        /* chipselect will always be inactive after setup() */
        return spi_setup(host->spi);
}

static int
mmc_spi_readbytes(struct mmc_spi_host *host, unsigned len)
{
        int status;

        if (len > sizeof(*host->data)) {
                WARN_ON(1);
                return -EIO;
        }

        host->status.len = len;

        if (host->dma_dev)
                dma_sync_single_for_device(host->dma_dev,
                                host->data_dma, sizeof(*host->data),
                                DMA_FROM_DEVICE);

        status = spi_sync(host->spi, &host->readback);

        if (host->dma_dev)
                dma_sync_single_for_cpu(host->dma_dev,
                                host->data_dma, sizeof(*host->data),
                                DMA_FROM_DEVICE);

        return status;
}

static int
mmc_spi_skip(struct mmc_spi_host *host, ktime_t timeout, unsigned n, u8 byte)
{
        u8              *cp = host->data->status;

        timeout = ktime_add(timeout, ktime_get());

        while (1) {
                int             status;
                unsigned        i;

                status = mmc_spi_readbytes(host, n);
                if (status < 0)
                        return status;

                for (i = 0; i < n; i++) {
                        if (cp[i] != byte)
                                return cp[i];
                }

                /* REVISIT investigate msleep() to avoid busy-wait I/O
                 * in at least some cases.
                 */
                if (ktime_to_ns(ktime_sub(ktime_get(), timeout)) > 0)
                        break;
        }
        return -ETIMEDOUT;
}

static inline int
mmc_spi_wait_unbusy(struct mmc_spi_host *host, ktime_t timeout)
{
        return mmc_spi_skip(host, timeout, sizeof(host->data->status), 0);
}

static int mmc_spi_readtoken(struct mmc_spi_host *host, ktime_t timeout)
{
        return mmc_spi_skip(host, timeout, 1, 0xff);
}


/*
 * Note that for SPI, cmd->resp[0] is not the same data as "native" protocol
 * hosts return!  The low byte holds R1_SPI bits.  The next byte may hold
 * R2_SPI bits ... for SEND_STATUS, or after data read errors.
 *
 * cmd->resp[1] holds any four-byte response, for R3 (READ_OCR) and on
 * newer cards R7 (IF_COND).
 */

static char *maptype(struct mmc_command *cmd)
{
        switch (mmc_spi_resp_type(cmd)) {
        case MMC_RSP_SPI_R1:    return "R1";
        case MMC_RSP_SPI_R1B:   return "R1B";
        case MMC_RSP_SPI_R2:    return "R2/R5";
        case MMC_RSP_SPI_R3:    return "R3/R4/R7";
        default:                return "?";
        }
}

/* return zero, else negative errno after setting cmd->error */
static int mmc_spi_response_get(struct mmc_spi_host *host,
                struct mmc_command *cmd, int cs_on)
{
        u8      *cp = host->data->status;
        u8      *end = cp + host->t.len;
        int     value = 0;
        char    tag[32];

        snprintf(tag, sizeof(tag), "  ... CMD%d response SPI_%s",
                cmd->opcode, maptype(cmd));

        /* Except for data block reads, the whole response will already
         * be stored in the scratch buffer.  It's somewhere after the
         * command and the first byte we read after it.  We ignore that
         * first byte.  After STOP_TRANSMISSION command it may include
         * two data bits, but otherwise it's all ones.
         */
        cp += 8;
        while (cp < end && *cp == 0xff)
                cp++;

        /* Data block reads (R1 response types) may need more data... */
        if (cp == end) {
                unsigned        i;

                cp = host->data->status;

                /* Card sends N(CR) (== 1..8) bytes of all-ones then one
                 * status byte ... and we already scanned 2 bytes.
                 *
                 * REVISIT block read paths use nasty byte-at-a-time I/O
                 * so it can always DMA directly into the target buffer.
                 * It'd probably be better to memcpy() the first chunk and
                 * avoid extra i/o calls...
                 */
                for (i = 2; i < 9; i++) {
                        value = mmc_spi_readbytes(host, 1);
                        if (value < 0)
                                goto done;
                        if (*cp != 0xff)
                                goto checkstatus;
                }
                value = -ETIMEDOUT;
                goto done;
        }

checkstatus:
        if (*cp & 0x80) {
                dev_dbg(&host->spi->dev, "%s: INVALID RESPONSE, %02x\n",
                                        tag, *cp);
                value = -EBADR;
                goto done;
        }

        cmd->resp[0] = *cp++;
        cmd->error = 0;

        /* Status byte: the entire seven-bit R1 response.  */
        if (cmd->resp[0] != 0) {
                if ((R1_SPI_PARAMETER | R1_SPI_ADDRESS
                                        | R1_SPI_ILLEGAL_COMMAND)
                                & cmd->resp[0])
                        value = -EINVAL;
                else if (R1_SPI_COM_CRC & cmd->resp[0])
                        value = -EILSEQ;
                else if ((R1_SPI_ERASE_SEQ | R1_SPI_ERASE_RESET)
                                & cmd->resp[0])
                        value = -EIO;
                /* else R1_SPI_IDLE, "it's resetting" */
        }

        switch (mmc_spi_resp_type(cmd)) {

        /* SPI R1B == R1 + busy; STOP_TRANSMISSION (for multiblock reads)
         * and less-common stuff like various erase operations.
         */
        case MMC_RSP_SPI_R1B:
                /* maybe we read all the busy tokens already */
                while (cp < end && *cp == 0)
                        cp++;
                if (cp == end)
                        mmc_spi_wait_unbusy(host, r1b_timeout);
                break;

        /* SPI R2 == R1 + second status byte; SEND_STATUS
         * SPI R5 == R1 + data byte; IO_RW_DIRECT
         */
        case MMC_RSP_SPI_R2:
                cmd->resp[0] |= *cp << 8;
                break;

        /* SPI R3, R4, or R7 == R1 + 4 bytes */
        case MMC_RSP_SPI_R3:
                cmd->resp[1] = get_unaligned_be32(cp);
                break;

        /* SPI R1 == just one status byte */
        case MMC_RSP_SPI_R1:
                break;

        default:
                dev_dbg(&host->spi->dev, "bad response type %04x\n",
                                mmc_spi_resp_type(cmd));
                if (value >= 0)
                        value = -EINVAL;
                goto done;
        }

        if (value < 0)
                dev_dbg(&host->spi->dev, "%s: resp %04x %08x\n",
                        tag, cmd->resp[0], cmd->resp[1]);

        /* disable chipselect on errors and some success cases */
        if (value >= 0 && cs_on)
                return value;
done:
        if (value < 0)
                cmd->error = value;
        mmc_cs_off(host);
        return value;
}

/* Issue command and read its response.
 * Returns zero on success, negative for error.
 *
 * On error, caller must cope with mmc core retry mechanism.  That
 * means immediate low-level resubmit, which affects the bus lock...
 */
static int
mmc_spi_command_send(struct mmc_spi_host *host,
                struct mmc_request *mrq,
                struct mmc_command *cmd, int cs_on)
{
        struct scratch          *data = host->data;
        u8                      *cp = data->status;
        u32                     arg = cmd->arg;
        int                     status;
        struct spi_transfer     *t;

        /* We can handle most commands (except block reads) in one full
         * duplex I/O operation before either starting the next transfer
         * (data block or command) or else deselecting the card.
         *
         * First, write 7 bytes:
         *  - an all-ones byte to ensure the card is ready
         *  - opcode byte (plus start and transmission bits)
         *  - four bytes of big-endian argument
         *  - crc7 (plus end bit) ... always computed, it's cheap
         *
         * We init the whole buffer to all-ones, which is what we need
         * to write while we're reading (later) response data.
         */
        memset(cp++, 0xff, sizeof(data->status));

        *cp++ = 0x40 | cmd->opcode;
        *cp++ = (u8)(arg >> 24);
        *cp++ = (u8)(arg >> 16);
        *cp++ = (u8)(arg >> 8);
        *cp++ = (u8)arg;
        *cp++ = (crc7(0, &data->status[1], 5) << 1) | 0x01;

        /* Then, read up to 13 bytes (while writing all-ones):
         *  - N(CR) (== 1..8) bytes of all-ones
         *  - status byte (for all response types)
         *  - the rest of the response, either:
         *      + nothing, for R1 or R1B responses
         *      + second status byte, for R2 responses
         *      + four data bytes, for R3 and R7 responses
         *
         * Finally, read some more bytes ... in the nice cases we know in
         * advance how many, and reading 1 more is always OK:
         *  - N(EC) (== 0..N) bytes of all-ones, before deselect/finish
         *  - N(RC) (== 1..N) bytes of all-ones, before next command
         *  - N(WR) (== 1..N) bytes of all-ones, before data write
         *
         * So in those cases one full duplex I/O of at most 21 bytes will
         * handle the whole command, leaving the card ready to receive a
         * data block or new command.  We do that whenever we can, shaving
         * CPU and IRQ costs (especially when using DMA or FIFOs).
         *
         * There are two other cases, where it's not generally practical
         * to rely on a single I/O:
         *
         *  - R1B responses need at least N(EC) bytes of all-zeroes.
         *
         *    In this case we can *try* to fit it into one I/O, then
         *    maybe read more data later.
         *
         *  - Data block reads are more troublesome, since a variable
         *    number of padding bytes precede the token and data.
         *      + N(CX) (== 0..8) bytes of all-ones, before CSD or CID
         *      + N(AC) (== 1..many) bytes of all-ones
         *
         *    In this case we currently only have minimal speedups here:
         *    when N(CR) == 1 we can avoid I/O in response_get().
         */
        if (cs_on && (mrq->data->flags & MMC_DATA_READ)) {
                cp += 2;        /* min(N(CR)) + status */
                /* R1 */
        } else {
                cp += 10;       /* max(N(CR)) + status + min(N(RC),N(WR)) */
                if (cmd->flags & MMC_RSP_SPI_S2)        /* R2/R5 */
                        cp++;
                else if (cmd->flags & MMC_RSP_SPI_B4)   /* R3/R4/R7 */
                        cp += 4;
                else if (cmd->flags & MMC_RSP_BUSY)     /* R1B */
                        cp = data->status + sizeof(data->status);
                /* else:  R1 (most commands) */
        }

        dev_dbg(&host->spi->dev, "  mmc_spi: CMD%d, resp %s\n",
                cmd->opcode, maptype(cmd));

        /* send command, leaving chipselect active */
        spi_message_init(&host->m);

        t = &host->t;
        memset(t, 0, sizeof(*t));
        t->tx_buf = t->rx_buf = data->status;
        t->tx_dma = t->rx_dma = host->data_dma;
        t->len = cp - data->status;
        t->cs_change = 1;
        spi_message_add_tail(t, &host->m);

        if (host->dma_dev) {
                host->m.is_dma_mapped = 1;
                dma_sync_single_for_device(host->dma_dev,
                                host->data_dma, sizeof(*host->data),
                                DMA_BIDIRECTIONAL);
        }
        status = spi_sync(host->spi, &host->m);

        if (host->dma_dev)
                dma_sync_single_for_cpu(host->dma_dev,
                                host->data_dma, sizeof(*host->data),
                                DMA_BIDIRECTIONAL);
        if (status < 0) {
                dev_dbg(&host->spi->dev, "  ... write returned %d\n", status);
                cmd->error = status;
                return status;
        }

        /* after no-data commands and STOP_TRANSMISSION, chipselect off */
        return mmc_spi_response_get(host, cmd, cs_on);
}

/* Build data message with up to four separate transfers.  For TX, we
 * start by writing the data token.  And in most cases, we finish with
 * a status transfer.
 *
 * We always provide TX data for data and CRC.  The MMC/SD protocol
 * requires us to write ones; but Linux defaults to writing zeroes;
 * so we explicitly initialize it to all ones on RX paths.
 *
 * We also handle DMA mapping, so the underlying SPI controller does
 * not need to (re)do it for each message.
 */
static void
mmc_spi_setup_data_message(
        struct mmc_spi_host     *host,
        int                     multiple,
        enum dma_data_direction direction)
{
        struct spi_transfer     *t;
        struct scratch          *scratch = host->data;
        dma_addr_t              dma = host->data_dma;

        spi_message_init(&host->m);
        if (dma)
                host->m.is_dma_mapped = 1;

        /* for reads, readblock() skips 0xff bytes before finding
         * the token; for writes, this transfer issues that token.
         */
        if (direction == DMA_TO_DEVICE) {
                t = &host->token;
                memset(t, 0, sizeof(*t));
                t->len = 1;
                if (multiple)
                        scratch->data_token = SPI_TOKEN_MULTI_WRITE;
                else
                        scratch->data_token = SPI_TOKEN_SINGLE;
                t->tx_buf = &scratch->data_token;
                if (dma)
                        t->tx_dma = dma + offsetof(struct scratch, data_token);
                spi_message_add_tail(t, &host->m);
        }

        /* Body of transfer is buffer, then CRC ...
         * either TX-only, or RX with TX-ones.
         */
        t = &host->t;
        memset(t, 0, sizeof(*t));
        t->tx_buf = host->ones;
        t->tx_dma = host->ones_dma;
        /* length and actual buffer info are written later */
        spi_message_add_tail(t, &host->m);

        t = &host->crc;
        memset(t, 0, sizeof(*t));
        t->len = 2;
        if (direction == DMA_TO_DEVICE) {
                /* the actual CRC may get written later */
                t->tx_buf = &scratch->crc_val;
                if (dma)
                        t->tx_dma = dma + offsetof(struct scratch, crc_val);
        } else {
                t->tx_buf = host->ones;
                t->tx_dma = host->ones_dma;
                t->rx_buf = &scratch->crc_val;
                if (dma)
                        t->rx_dma = dma + offsetof(struct scratch, crc_val);
        }
        spi_message_add_tail(t, &host->m);

        /*
         * A single block read is followed by N(EC) [0+] all-ones bytes
         * before deselect ... don't bother.
         *
         * Multiblock reads are followed by N(AC) [1+] all-ones bytes before
         * the next block is read, or a STOP_TRANSMISSION is issued.  We'll
         * collect that single byte, so readblock() doesn't need to.
         *
         * For a write, the one-byte data response follows immediately, then
         * come zero or more busy bytes, then N(WR) [1+] all-ones bytes.
         * Then single block reads may deselect, and multiblock ones issue
         * the next token (next data block, or STOP_TRAN).  We can try to
         * minimize I/O ops by using a single read to collect end-of-busy.
         */
        if (multiple || direction == DMA_TO_DEVICE) {
                t = &host->early_status;
                memset(t, 0, sizeof(*t));
                t->len = (direction == DMA_TO_DEVICE)
                                ? sizeof(scratch->status)
                                : 1;
                t->tx_buf = host->ones;
                t->tx_dma = host->ones_dma;
                t->rx_buf = scratch->status;
                if (dma)
                        t->rx_dma = dma + offsetof(struct scratch, status);
                t->cs_change = 1;
                spi_message_add_tail(t, &host->m);
        }
}

/*
 * Write one block:
 *  - caller handled preceding N(WR) [1+] all-ones bytes
 *  - data block
 *      + token
 *      + data bytes
 *      + crc16
 *  - an all-ones byte ... card writes a data-response byte
 *  - followed by N(EC) [0+] all-ones bytes, card writes zero/'busy'
 *
 * Return negative errno, else success.
 */
static int
mmc_spi_writeblock(struct mmc_spi_host *host, struct spi_transfer *t,
        ktime_t timeout)
{
        struct spi_device       *spi = host->spi;
        int                     status, i;
        struct scratch          *scratch = host->data;

        if (host->mmc->use_spi_crc)
                scratch->crc_val = cpu_to_be16(
                                crc_itu_t(0, t->tx_buf, t->len));
        if (host->dma_dev)
                dma_sync_single_for_device(host->dma_dev,
                                host->data_dma, sizeof(*scratch),
                                DMA_BIDIRECTIONAL);

        status = spi_sync(spi, &host->m);

        if (status != 0) {
                dev_dbg(&spi->dev, "write error (%d)\n", status);
                return status;
        }

        if (host->dma_dev)
                dma_sync_single_for_cpu(host->dma_dev,
                                host->data_dma, sizeof(*scratch),
                                DMA_BIDIRECTIONAL);

        /*
         * Get the transmission data-response reply.  It must follow
         * immediately after the data block we transferred.  This reply
         * doesn't necessarily tell whether the write operation succeeded;
         * it just says if the transmission was ok and whether *earlier*
         * writes succeeded; see the standard.
         */
        switch (SPI_MMC_RESPONSE_CODE(scratch->status[0])) {
        case SPI_RESPONSE_ACCEPTED:
                status = 0;
                break;
        case SPI_RESPONSE_CRC_ERR:
                /* host shall then issue MMC_STOP_TRANSMISSION */
                status = -EILSEQ;
                break;
        case SPI_RESPONSE_WRITE_ERR:
                /* host shall then issue MMC_STOP_TRANSMISSION,
                 * and should MMC_SEND_STATUS to sort it out
                 */
                status = -EIO;
                break;
        default:
                status = -EPROTO;
                break;
        }
        if (status != 0) {
                dev_dbg(&spi->dev, "write error %02x (%d)\n",
                        scratch->status[0], status);
                return status;
        }

        t->tx_buf += t->len;
        if (host->dma_dev)
                t->tx_dma += t->len;

        /* Return when not busy.  If we didn't collect that status yet,
         * we'll need some more I/O.
         */
        for (i = 1; i < sizeof(scratch->status); i++) {
                if (scratch->status[i] != 0)
                        return 0;
        }
        return mmc_spi_wait_unbusy(host, timeout);
}

/*
 * Read one block:
 *  - skip leading all-ones bytes ... either
 *      + N(AC) [1..f(clock,CSD)] usually, else
 *      + N(CX) [0..8] when reading CSD or CID
 *  - data block
 *      + token ... if error token, no data or crc
 *      + data bytes
 *      + crc16
 *
 * After single block reads, we're done; N(EC) [0+] all-ones bytes follow
 * before dropping chipselect.
 *
 * For multiblock reads, caller either reads the next block or issues a
 * STOP_TRANSMISSION command.
 */
static int
mmc_spi_readblock(struct mmc_spi_host *host, struct spi_transfer *t,
        ktime_t timeout)
{
        struct spi_device       *spi = host->spi;
        int                     status;
        struct scratch          *scratch = host->data;

        /* At least one SD card sends an all-zeroes byte when N(CX)
         * applies, before the all-ones bytes ... just cope with that.
         */
        status = mmc_spi_readbytes(host, 1);
        if (status < 0)
                return status;
        status = scratch->status[0];
        if (status == 0xff || status == 0)
                status = mmc_spi_readtoken(host, timeout);

        if (status == SPI_TOKEN_SINGLE) {
                if (host->dma_dev) {
                        dma_sync_single_for_device(host->dma_dev,
                                        host->data_dma, sizeof(*scratch),
                                        DMA_BIDIRECTIONAL);
                        dma_sync_single_for_device(host->dma_dev,
                                        t->rx_dma, t->len,
                                        DMA_FROM_DEVICE);
                }

                status = spi_sync(spi, &host->m);

                if (host->dma_dev) {
                        dma_sync_single_for_cpu(host->dma_dev,
                                        host->data_dma, sizeof(*scratch),
                                        DMA_BIDIRECTIONAL);
                        dma_sync_single_for_cpu(host->dma_dev,
                                        t->rx_dma, t->len,
                                        DMA_FROM_DEVICE);
                }

        } else {
                dev_dbg(&spi->dev, "read error %02x (%d)\n", status, status);

                /* we've read extra garbage, timed out, etc */
                if (status < 0)
                        return status;

                /* low four bits are an R2 subset, fifth seems to be
                 * vendor specific ... map them all to generic error..
                 */
                return -EIO;
        }

        if (host->mmc->use_spi_crc) {
                u16 crc = crc_itu_t(0, t->rx_buf, t->len);

                be16_to_cpus(&scratch->crc_val);
                if (scratch->crc_val != crc) {
                        dev_dbg(&spi->dev, "read - crc error: crc_val=0x%04x, "
                                        "computed=0x%04x len=%d\n",
                                        scratch->crc_val, crc, t->len);
                        return -EILSEQ;
                }
        }

        t->rx_buf += t->len;
        if (host->dma_dev)
                t->rx_dma += t->len;

        return 0;
}

/*
 * An MMC/SD data stage includes one or more blocks, optional CRCs,
 * and inline handshaking.  That handhaking makes it unlike most
 * other SPI protocol stacks.
 */
static void
mmc_spi_data_do(struct mmc_spi_host *host, struct mmc_command *cmd,
                struct mmc_data *data, u32 blk_size)
{
        struct spi_device       *spi = host->spi;
        struct device           *dma_dev = host->dma_dev;
        struct spi_transfer     *t;
        enum dma_data_direction direction;
        struct scatterlist      *sg;
        unsigned                n_sg;
        int                     multiple = (data->blocks > 1);
        u32                     clock_rate;
        ktime_t                 timeout;

        if (data->flags & MMC_DATA_READ)
                direction = DMA_FROM_DEVICE;
        else
                direction = DMA_TO_DEVICE;
        mmc_spi_setup_data_message(host, multiple, direction);
        t = &host->t;

        if (t->speed_hz)
                clock_rate = t->speed_hz;
        else
                clock_rate = spi->max_speed_hz;

        timeout = ktime_add_ns(ktime_set(0, 0), data->timeout_ns +
                        data->timeout_clks * 1000000 / clock_rate);

        /* Handle scatterlist segments one at a time, with synch for
         * each 512-byte block
         */
        for (sg = data->sg, n_sg = data->sg_len; n_sg; n_sg--, sg++) {
                int                     status = 0;
                dma_addr_t              dma_addr = 0;
                void                    *kmap_addr;
                unsigned                length = sg->length;
                enum dma_data_direction dir = direction;

                /* set up dma mapping for controller drivers that might
                 * use DMA ... though they may fall back to PIO
                 */
                if (dma_dev) {
                        /* never invalidate whole *shared* pages ... */
                        if ((sg->offset != 0 || length != PAGE_SIZE)
                                        && dir == DMA_FROM_DEVICE)
                                dir = DMA_BIDIRECTIONAL;

                        dma_addr = dma_map_page(dma_dev, sg_page(sg), 0,
                                                PAGE_SIZE, dir);
                        if (direction == DMA_TO_DEVICE)
                                t->tx_dma = dma_addr + sg->offset;
                        else
                                t->rx_dma = dma_addr + sg->offset;
                }

                /* allow pio too; we don't allow highmem */
                kmap_addr = kmap(sg_page(sg));
                if (direction == DMA_TO_DEVICE)
                        t->tx_buf = kmap_addr + sg->offset;
                else
                        t->rx_buf = kmap_addr + sg->offset;

                /* transfer each block, and update request status */
                while (length) {
                        t->len = min(length, blk_size);

                        dev_dbg(&host->spi->dev,
                                "    mmc_spi: %s block, %d bytes\n",
                                (direction == DMA_TO_DEVICE)
                                ? "write"
                                : "read",
                                t->len);

                        if (direction == DMA_TO_DEVICE)
                                status = mmc_spi_writeblock(host, t, timeout);
                        else
                                status = mmc_spi_readblock(host, t, timeout);
                        if (status < 0)
                                break;

                        data->bytes_xfered += t->len;
                        length -= t->len;

                        if (!multiple)
                                break;
                }

                /* discard mappings */
                if (direction == DMA_FROM_DEVICE)
                        flush_kernel_dcache_page(sg_page(sg));
                kunmap(sg_page(sg));
                if (dma_dev)
                        dma_unmap_page(dma_dev, dma_addr, PAGE_SIZE, dir);

                if (status < 0) {
                        data->error = status;
                        dev_dbg(&spi->dev, "%s status %d\n",
                                (direction == DMA_TO_DEVICE)
                                        ? "write" : "read",
                                status);
                        break;
                }
        }

        /* NOTE some docs describe an MMC-only SET_BLOCK_COUNT (CMD23) that
         * can be issued before multiblock writes.  Unlike its more widely
         * documented analogue for SD cards (SET_WR_BLK_ERASE_COUNT, ACMD23),
         * that can affect the STOP_TRAN logic.   Complete (and current)
         * MMC specs should sort that out before Linux starts using CMD23.
         */
        if (direction == DMA_TO_DEVICE && multiple) {
                struct scratch  *scratch = host->data;
                int             tmp;
                const unsigned  statlen = sizeof(scratch->status);

                dev_dbg(&spi->dev, "    mmc_spi: STOP_TRAN\n");

                /* Tweak the per-block message we set up earlier by morphing
                 * it to hold single buffer with the token followed by some
                 * all-ones bytes ... skip N(BR) (0..1), scan the rest for
                 * "not busy any longer" status, and leave chip selected.
                 */
                INIT_LIST_HEAD(&host->m.transfers);
                list_add(&host->early_status.transfer_list,
                                &host->m.transfers);

                memset(scratch->status, 0xff, statlen);
                scratch->status[0] = SPI_TOKEN_STOP_TRAN;

                host->early_status.tx_buf = host->early_status.rx_buf;
                host->early_status.tx_dma = host->early_status.rx_dma;
                host->early_status.len = statlen;

                if (host->dma_dev)
                        dma_sync_single_for_device(host->dma_dev,
                                        host->data_dma, sizeof(*scratch),
                                        DMA_BIDIRECTIONAL);

                tmp = spi_sync(spi, &host->m);

                if (host->dma_dev)
                        dma_sync_single_for_cpu(host->dma_dev,
                                        host->data_dma, sizeof(*scratch),
                                        DMA_BIDIRECTIONAL);

                if (tmp < 0) {
                        if (!data->error)
                                data->error = tmp;
                        return;
                }

                /* Ideally we collected "not busy" status with one I/O,
                 * avoiding wasteful byte-at-a-time scanning... but more
                 * I/O is often needed.
                 */
                for (tmp = 2; tmp < statlen; tmp++) {
                        if (scratch->status[tmp] != 0)
                                return;
                }
                tmp = mmc_spi_wait_unbusy(host, timeout);
                if (tmp < 0 && !data->error)
                        data->error = tmp;
        }
}

/****************************************************************************/

/*
 * MMC driver implementation -- the interface to the MMC stack
 */

static void mmc_spi_request(struct mmc_host *mmc, struct mmc_request *mrq)
{
        struct mmc_spi_host     *host = mmc_priv(mmc);
        int                     status = -EINVAL;

#ifdef DEBUG
        /* MMC core and layered drivers *MUST* issue SPI-aware commands */
        {
                struct mmc_command      *cmd;
                int                     invalid = 0;

                cmd = mrq->cmd;
                if (!mmc_spi_resp_type(cmd)) {
                        dev_dbg(&host->spi->dev, "bogus command\n");
                        cmd->error = -EINVAL;
                        invalid = 1;
                }

                cmd = mrq->stop;
                if (cmd && !mmc_spi_resp_type(cmd)) {
                        dev_dbg(&host->spi->dev, "bogus STOP command\n");
                        cmd->error = -EINVAL;
                        invalid = 1;
                }

                if (invalid) {
                        dump_stack();
                        mmc_request_done(host->mmc, mrq);
                        return;
                }
        }
#endif

        /* issue command; then optionally data and stop */
        status = mmc_spi_command_send(host, mrq, mrq->cmd, mrq->data != NULL);
        if (status == 0 && mrq->data) {
                mmc_spi_data_do(host, mrq->cmd, mrq->data, mrq->data->blksz);
                if (mrq->stop)
                        status = mmc_spi_command_send(host, mrq, mrq->stop, 0);
                else
                        mmc_cs_off(host);
        }

        mmc_request_done(host->mmc, mrq);
}

/* See Section 6.4.1, in SD "Simplified Physical Layer Specification 2.0"
 *
 * NOTE that here we can't know that the card has just been powered up;
 * not all MMC/SD sockets support power switching.
 *
 * FIXME when the card is still in SPI mode, e.g. from a previous kernel,
 * this doesn't seem to do the right thing at all...
 */
static void mmc_spi_initsequence(struct mmc_spi_host *host)
{
        /* Try to be very sure any previous command has completed;
         * wait till not-busy, skip debris from any old commands.
         */
        mmc_spi_wait_unbusy(host, r1b_timeout);
        mmc_spi_readbytes(host, 10);

        /*
         * Do a burst with chipselect active-high.  We need to do this to
         * meet the requirement of 74 clock cycles with both chipselect
         * and CMD (MOSI) high before CMD0 ... after the card has been
         * powered up to Vdd(min), and so is ready to take commands.
         *
         * Some cards are particularly needy of this (e.g. Viking "SD256")
         * while most others don't seem to care.
         *
         * Note that this is one of the places MMC/SD plays games with the
         * SPI protocol.  Another is that when chipselect is released while
         * the card returns BUSY status, the clock must issue several cycles
         * with chipselect high before the card will stop driving its output.
         */
        host->spi->mode |= SPI_CS_HIGH;
        if (spi_setup(host->spi) != 0) {
                /* Just warn; most cards work without it. */
                dev_warn(&host->spi->dev,
                                "can't change chip-select polarity\n");
                host->spi->mode &= ~SPI_CS_HIGH;
        } else {
                mmc_spi_readbytes(host, 18);

                host->spi->mode &= ~SPI_CS_HIGH;
                if (spi_setup(host->spi) != 0) {
                        /* Wot, we can't get the same setup we had before? */
                        dev_err(&host->spi->dev,
                                        "can't restore chip-select polarity\n");
                }
        }
}

static char *mmc_powerstring(u8 power_mode)
{
        switch (power_mode) {
        case MMC_POWER_OFF: return "off";
        case MMC_POWER_UP:  return "up";
        case MMC_POWER_ON:  return "on";
        }
        return "?";
}

static void mmc_spi_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
{
        struct mmc_spi_host *host = mmc_priv(mmc);

        if (host->power_mode != ios->power_mode) {
                int             canpower;

                canpower = host->pdata && host->pdata->setpower;

                dev_dbg(&host->spi->dev, "mmc_spi: power %s (%d)%s\n",
                                mmc_powerstring(ios->power_mode),
                                ios->vdd,
                                canpower ? ", can switch" : "");

                /* switch power on/off if possible, accounting for
                 * max 250msec powerup time if needed.
                 */
                if (canpower) {
                        switch (ios->power_mode) {
                        case MMC_POWER_OFF:
                        case MMC_POWER_UP:
                                host->pdata->setpower(&host->spi->dev,
                                                ios->vdd);
                                if (ios->power_mode == MMC_POWER_UP)
                                        msleep(host->powerup_msecs);
                        }
                }

                /* See 6.4.1 in the simplified SD card physical spec 2.0 */
                if (ios->power_mode == MMC_POWER_ON)
                        mmc_spi_initsequence(host);

                /* If powering down, ground all card inputs to avoid power
                 * delivery from data lines!  On a shared SPI bus, this
                 * will probably be temporary; 6.4.2 of the simplified SD
                 * spec says this must last at least 1msec.
                 *
                 *   - Clock low means CPOL 0, e.g. mode 0
                 *   - MOSI low comes from writing zero
                 *   - Chipselect is usually active low...
                 */
                if (canpower && ios->power_mode == MMC_POWER_OFF) {
                        int mres;
                        u8 nullbyte = 0;

                        host->spi->mode &= ~(SPI_CPOL|SPI_CPHA);
                        mres = spi_setup(host->spi);
                        if (mres < 0)
                                dev_dbg(&host->spi->dev,
                                        "switch to SPI mode 0 failed\n");

                        if (spi_write(host->spi, &nullbyte, 1) < 0)
                                dev_dbg(&host->spi->dev,
                                        "put spi signals to low failed\n");

                        /*
                         * Now clock should be low due to spi mode 0;
                         * MOSI should be low because of written 0x00;
                         * chipselect should be low (it is active low)
                         * power supply is off, so now MMC is off too!
                         *
                         * FIXME no, chipselect can be high since the
                         * device is inactive and SPI_CS_HIGH is clear...
                         */
                        msleep(10);
                        if (mres == 0) {
                                host->spi->mode |= (SPI_CPOL|SPI_CPHA);
                                mres = spi_setup(host->spi);
                                if (mres < 0)
                                        dev_dbg(&host->spi->dev,
                                                "switch back to SPI mode 3"
                                                " failed\n");
                        }
                }

                host->power_mode = ios->power_mode;
        }

        if (host->spi->max_speed_hz != ios->clock && ios->clock != 0) {
                int             status;

                host->spi->max_speed_hz = ios->clock;
                status = spi_setup(host->spi);
                dev_dbg(&host->spi->dev,
                        "mmc_spi:  clock to %d Hz, %d\n",
                        host->spi->max_speed_hz, status);
        }
}

static int mmc_spi_get_ro(struct mmc_host *mmc)
{
        struct mmc_spi_host *host = mmc_priv(mmc);

        if (host->pdata && host->pdata->get_ro)
                return !!host->pdata->get_ro(mmc->parent);
        /*
         * Board doesn't support read only detection; let the mmc core
         * decide what to do.
         */
        return -ENOSYS;
}

static int mmc_spi_get_cd(struct mmc_host *mmc)
{
        struct mmc_spi_host *host = mmc_priv(mmc);

        if (host->pdata && host->pdata->get_cd)
                return !!host->pdata->get_cd(mmc->parent);
        return -ENOSYS;
}

static const struct mmc_host_ops mmc_spi_ops = {
        .request        = mmc_spi_request,
        .set_ios        = mmc_spi_set_ios,
        .get_ro         = mmc_spi_get_ro,
        .get_cd         = mmc_spi_get_cd,
};


/****************************************************************************/

/*
 * SPI driver implementation
 */

static irqreturn_t
mmc_spi_detect_irq(int irq, void *mmc)
{
        struct mmc_spi_host *host = mmc_priv(mmc);
        u16 delay_msec = max(host->pdata->detect_delay, (u16)100);

        mmc_detect_change(mmc, msecs_to_jiffies(delay_msec));
        return IRQ_HANDLED;
}

struct count_children {
        unsigned        n;
        struct bus_type *bus;
};

static int maybe_count_child(struct device *dev, void *c)
{
        struct count_children *ccp = c;

        if (dev->bus == ccp->bus) {
                if (ccp->n)
                        return -EBUSY;
                ccp->n++;
        }
        return 0;
}

static int mmc_spi_probe(struct spi_device *spi)
{
        void                    *ones;
        struct mmc_host         *mmc;
        struct mmc_spi_host     *host;
        int                     status;

        /* MMC and SD specs only seem to care that sampling is on the
         * rising edge ... meaning SPI modes 0 or 3.  So either SPI mode
         * should be legit.  We'll use mode 0 since it seems to be a
         * bit less troublesome on some hardware ... unclear why.
         */
        spi->mode = SPI_MODE_0;
        spi->bits_per_word = 8;

        status = spi_setup(spi);
        if (status < 0) {
                dev_dbg(&spi->dev, "needs SPI mode %02x, %d KHz; %d\n",
                                spi->mode, spi->max_speed_hz / 1000,
                                status);
                return status;
        }

        /* We can use the bus safely iff nobody else will interfere with us.
         * Most commands consist of one SPI message to issue a command, then
         * several more to collect its response, then possibly more for data
         * transfer.  Clocking access to other devices during that period will
         * corrupt the command execution.
         *
         * Until we have software primitives which guarantee non-interference,
         * we'll aim for a hardware-level guarantee.
         *
         * REVISIT we can't guarantee another device won't be added later...
         */
        if (spi->master->num_chipselect > 1) {
                struct count_children cc;

                cc.n = 0;
                cc.bus = spi->dev.bus;
                status = device_for_each_child(spi->dev.parent, &cc,
                                maybe_count_child);
                if (status < 0) {
                        dev_err(&spi->dev, "can't share SPI bus\n");
                        return status;
                }

                dev_warn(&spi->dev, "ASSUMING SPI bus stays unshared!\n");
        }

        /* We need a supply of ones to transmit.  This is the only time
         * the CPU touches these, so cache coherency isn't a concern.
         *
         * NOTE if many systems use more than one MMC-over-SPI connector
         * it'd save some memory to share this.  That's evidently rare.
         */
        status = -ENOMEM;
        ones = kmalloc(MMC_SPI_BLOCKSIZE, GFP_KERNEL);
        if (!ones)
                goto nomem;
        memset(ones, 0xff, MMC_SPI_BLOCKSIZE);

        mmc = mmc_alloc_host(sizeof(*host), &spi->dev);
        if (!mmc)
                goto nomem;

        mmc->ops = &mmc_spi_ops;
        mmc->max_blk_size = MMC_SPI_BLOCKSIZE;

        mmc->caps = MMC_CAP_SPI;

        /* SPI doesn't need the lowspeed device identification thing for
         * MMC or SD cards, since it never comes up in open drain mode.
         * That's good; some SPI masters can't handle very low speeds!
         *
         * However, low speed SDIO cards need not handle over 400 KHz;
         * that's the only reason not to use a few MHz for f_min (until
         * the upper layer reads the target frequency from the CSD).
         */
        mmc->f_min = 400000;
        mmc->f_max = spi->max_speed_hz;

        host = mmc_priv(mmc);
        host->mmc = mmc;
        host->spi = spi;

        host->ones = ones;

        /* Platform data is used to hook up things like card sensing
         * and power switching gpios.
         */
        host->pdata = spi->dev.platform_data;
        if (host->pdata)
                mmc->ocr_avail = host->pdata->ocr_mask;
        if (!mmc->ocr_avail) {
                dev_warn(&spi->dev, "ASSUMING 3.2-3.4 V slot power\n");
                mmc->ocr_avail = MMC_VDD_32_33|MMC_VDD_33_34;
        }
        if (host->pdata && host->pdata->setpower) {
                host->powerup_msecs = host->pdata->powerup_msecs;
                if (!host->powerup_msecs || host->powerup_msecs > 250)
                        host->powerup_msecs = 250;
        }

        dev_set_drvdata(&spi->dev, mmc);

        /* preallocate dma buffers */
        host->data = kmalloc(sizeof(*host->data), GFP_KERNEL);
        if (!host->data)
                goto fail_nobuf1;

        if (spi->master->dev.parent->dma_mask) {
                struct device   *dev = spi->master->dev.parent;

                host->dma_dev = dev;
                host->ones_dma = dma_map_single(dev, ones,
                                MMC_SPI_BLOCKSIZE, DMA_TO_DEVICE);
                host->data_dma = dma_map_single(dev, host->data,
                                sizeof(*host->data), DMA_BIDIRECTIONAL);

                /* REVISIT in theory those map operations can fail... */

                dma_sync_single_for_cpu(host->dma_dev,
                                host->data_dma, sizeof(*host->data),
                                DMA_BIDIRECTIONAL);
        }

        /* setup message for status/busy readback */
        spi_message_init(&host->readback);
        host->readback.is_dma_mapped = (host->dma_dev != NULL);

        spi_message_add_tail(&host->status, &host->readback);
        host->status.tx_buf = host->ones;
        host->status.tx_dma = host->ones_dma;
        host->status.rx_buf = &host->data->status;
        host->status.rx_dma = host->data_dma + offsetof(struct scratch, status);
        host->status.cs_change = 1;

        /* register card detect irq */
        if (host->pdata && host->pdata->init) {
                status = host->pdata->init(&spi->dev, mmc_spi_detect_irq, mmc);
                if (status != 0)
                        goto fail_glue_init;
        }

        /* pass platform capabilities, if any */
        if (host->pdata)
                mmc->caps |= host->pdata->caps;

        status = mmc_add_host(mmc);
        if (status != 0)
                goto fail_add_host;

        dev_info(&spi->dev, "SD/MMC host %s%s%s%s%s\n",
                        mmc->class_dev.bus_id,
                        host->dma_dev ? "" : ", no DMA",
                        (host->pdata && host->pdata->get_ro)
                                ? "" : ", no WP",
                        (host->pdata && host->pdata->setpower)
                                ? "" : ", no poweroff",
                        (mmc->caps & MMC_CAP_NEEDS_POLL)
                                ? ", cd polling" : "");
        return 0;

fail_add_host:
        mmc_remove_host (mmc);
fail_glue_init:
        if (host->dma_dev)
                dma_unmap_single(host->dma_dev, host->data_dma,
                                sizeof(*host->data), DMA_BIDIRECTIONAL);
        kfree(host->data);

fail_nobuf1:
        mmc_free_host(mmc);
        dev_set_drvdata(&spi->dev, NULL);

nomem:
        kfree(ones);
        return status;
}


static int __devexit mmc_spi_remove(struct spi_device *spi)
{
        struct mmc_host         *mmc = dev_get_drvdata(&spi->dev);
        struct mmc_spi_host     *host;

        if (mmc) {
                host = mmc_priv(mmc);

                /* prevent new mmc_detect_change() calls */
                if (host->pdata && host->pdata->exit)
                        host->pdata->exit(&spi->dev, mmc);

                mmc_remove_host(mmc);

                if (host->dma_dev) {
                        dma_unmap_single(host->dma_dev, host->ones_dma,
                                MMC_SPI_BLOCKSIZE, DMA_TO_DEVICE);
                        dma_unmap_single(host->dma_dev, host->data_dma,
                                sizeof(*host->data), DMA_BIDIRECTIONAL);
                }

                kfree(host->data);
                kfree(host->ones);

                spi->max_speed_hz = mmc->f_max;
                mmc_free_host(mmc);
                dev_set_drvdata(&spi->dev, NULL);
        }
        return 0;
}


static struct spi_driver mmc_spi_driver = {
        .driver = {
                .name =         "mmc_spi",
                .bus =          &spi_bus_type,
                .owner =        THIS_MODULE,
        },
        .probe =        mmc_spi_probe,
        .remove =       __devexit_p(mmc_spi_remove),
};


static int __init mmc_spi_init(void)
{
        return spi_register_driver(&mmc_spi_driver);
}
module_init(mmc_spi_init);


static void __exit mmc_spi_exit(void)
{
        spi_unregister_driver(&mmc_spi_driver);
}
module_exit(mmc_spi_exit);


MODULE_AUTHOR("Mike Lavender, David Brownell, "
                "Hans-Peter Nilsson, Jan Nikitenko");
MODULE_DESCRIPTION("SPI SD/MMC host driver");
MODULE_LICENSE("GPL");