Merge branch 'linus' into perfcounters/core

[linux-2.6] / arch / powerpc / kernel / perf_counter.c

/*
 * Performance counter support - powerpc architecture code
 *
 * Copyright 2008-2009 Paul Mackerras, IBM Corporation.
 *
 * 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.
 */
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/perf_counter.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <asm/reg.h>
#include <asm/pmc.h>
#include <asm/machdep.h>
#include <asm/firmware.h>
#include <asm/ptrace.h>

struct cpu_hw_counters {
        int n_counters;
        int n_percpu;
        int disabled;
        int n_added;
        int n_limited;
        u8  pmcs_enabled;
        struct perf_counter *counter[MAX_HWCOUNTERS];
        u64 events[MAX_HWCOUNTERS];
        unsigned int flags[MAX_HWCOUNTERS];
        u64 mmcr[3];
        struct perf_counter *limited_counter[MAX_LIMITED_HWCOUNTERS];
        u8  limited_hwidx[MAX_LIMITED_HWCOUNTERS];
};
DEFINE_PER_CPU(struct cpu_hw_counters, cpu_hw_counters);

struct power_pmu *ppmu;

/*
 * Normally, to ignore kernel events we set the FCS (freeze counters
 * in supervisor mode) bit in MMCR0, but if the kernel runs with the
 * hypervisor bit set in the MSR, or if we are running on a processor
 * where the hypervisor bit is forced to 1 (as on Apple G5 processors),
 * then we need to use the FCHV bit to ignore kernel events.
 */
static unsigned int freeze_counters_kernel = MMCR0_FCS;

static void perf_counter_interrupt(struct pt_regs *regs);

void perf_counter_print_debug(void)
{
}

/*
 * Read one performance monitor counter (PMC).
 */
static unsigned long read_pmc(int idx)
{
        unsigned long val;

        switch (idx) {
        case 1:
                val = mfspr(SPRN_PMC1);
                break;
        case 2:
                val = mfspr(SPRN_PMC2);
                break;
        case 3:
                val = mfspr(SPRN_PMC3);
                break;
        case 4:
                val = mfspr(SPRN_PMC4);
                break;
        case 5:
                val = mfspr(SPRN_PMC5);
                break;
        case 6:
                val = mfspr(SPRN_PMC6);
                break;
        case 7:
                val = mfspr(SPRN_PMC7);
                break;
        case 8:
                val = mfspr(SPRN_PMC8);
                break;
        default:
                printk(KERN_ERR "oops trying to read PMC%d\n", idx);
                val = 0;
        }
        return val;
}

/*
 * Write one PMC.
 */
static void write_pmc(int idx, unsigned long val)
{
        switch (idx) {
        case 1:
                mtspr(SPRN_PMC1, val);
                break;
        case 2:
                mtspr(SPRN_PMC2, val);
                break;
        case 3:
                mtspr(SPRN_PMC3, val);
                break;
        case 4:
                mtspr(SPRN_PMC4, val);
                break;
        case 5:
                mtspr(SPRN_PMC5, val);
                break;
        case 6:
                mtspr(SPRN_PMC6, val);
                break;
        case 7:
                mtspr(SPRN_PMC7, val);
                break;
        case 8:
                mtspr(SPRN_PMC8, val);
                break;
        default:
                printk(KERN_ERR "oops trying to write PMC%d\n", idx);
        }
}

/*
 * Check if a set of events can all go on the PMU at once.
 * If they can't, this will look at alternative codes for the events
 * and see if any combination of alternative codes is feasible.
 * The feasible set is returned in event[].
 */
static int power_check_constraints(u64 event[], unsigned int cflags[],
                                   int n_ev)
{
        u64 mask, value, nv;
        u64 alternatives[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
        u64 amasks[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
        u64 avalues[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
        u64 smasks[MAX_HWCOUNTERS], svalues[MAX_HWCOUNTERS];
        int n_alt[MAX_HWCOUNTERS], choice[MAX_HWCOUNTERS];
        int i, j;
        u64 addf = ppmu->add_fields;
        u64 tadd = ppmu->test_adder;

        if (n_ev > ppmu->n_counter)
                return -1;

        /* First see if the events will go on as-is */
        for (i = 0; i < n_ev; ++i) {
                if ((cflags[i] & PPMU_LIMITED_PMC_REQD)
                    && !ppmu->limited_pmc_event(event[i])) {
                        ppmu->get_alternatives(event[i], cflags[i],
                                               alternatives[i]);
                        event[i] = alternatives[i][0];
                }
                if (ppmu->get_constraint(event[i], &amasks[i][0],
                                         &avalues[i][0]))
                        return -1;
        }
        value = mask = 0;
        for (i = 0; i < n_ev; ++i) {
                nv = (value | avalues[i][0]) + (value & avalues[i][0] & addf);
                if ((((nv + tadd) ^ value) & mask) != 0 ||
                    (((nv + tadd) ^ avalues[i][0]) & amasks[i][0]) != 0)
                        break;
                value = nv;
                mask |= amasks[i][0];
        }
        if (i == n_ev)
                return 0;       /* all OK */

        /* doesn't work, gather alternatives... */
        if (!ppmu->get_alternatives)
                return -1;
        for (i = 0; i < n_ev; ++i) {
                choice[i] = 0;
                n_alt[i] = ppmu->get_alternatives(event[i], cflags[i],
                                                  alternatives[i]);
                for (j = 1; j < n_alt[i]; ++j)
                        ppmu->get_constraint(alternatives[i][j],
                                             &amasks[i][j], &avalues[i][j]);
        }

        /* enumerate all possibilities and see if any will work */
        i = 0;
        j = -1;
        value = mask = nv = 0;
        while (i < n_ev) {
                if (j >= 0) {
                        /* we're backtracking, restore context */
                        value = svalues[i];
                        mask = smasks[i];
                        j = choice[i];
                }
                /*
                 * See if any alternative k for event i,
                 * where k > j, will satisfy the constraints.
                 */
                while (++j < n_alt[i]) {
                        nv = (value | avalues[i][j]) +
                                (value & avalues[i][j] & addf);
                        if ((((nv + tadd) ^ value) & mask) == 0 &&
                            (((nv + tadd) ^ avalues[i][j])
                             & amasks[i][j]) == 0)
                                break;
                }
                if (j >= n_alt[i]) {
                        /*
                         * No feasible alternative, backtrack
                         * to event i-1 and continue enumerating its
                         * alternatives from where we got up to.
                         */
                        if (--i < 0)
                                return -1;
                } else {
                        /*
                         * Found a feasible alternative for event i,
                         * remember where we got up to with this event,
                         * go on to the next event, and start with
                         * the first alternative for it.
                         */
                        choice[i] = j;
                        svalues[i] = value;
                        smasks[i] = mask;
                        value = nv;
                        mask |= amasks[i][j];
                        ++i;
                        j = -1;
                }
        }

        /* OK, we have a feasible combination, tell the caller the solution */
        for (i = 0; i < n_ev; ++i)
                event[i] = alternatives[i][choice[i]];
        return 0;
}

/*
 * Check if newly-added counters have consistent settings for
 * exclude_{user,kernel,hv} with each other and any previously
 * added counters.
 */
static int check_excludes(struct perf_counter **ctrs, unsigned int cflags[],
                          int n_prev, int n_new)
{
        int eu = 0, ek = 0, eh = 0;
        int i, n, first;
        struct perf_counter *counter;

        n = n_prev + n_new;
        if (n <= 1)
                return 0;

        first = 1;
        for (i = 0; i < n; ++i) {
                if (cflags[i] & PPMU_LIMITED_PMC_OK) {
                        cflags[i] &= ~PPMU_LIMITED_PMC_REQD;
                        continue;
                }
                counter = ctrs[i];
                if (first) {
                        eu = counter->attr.exclude_user;
                        ek = counter->attr.exclude_kernel;
                        eh = counter->attr.exclude_hv;
                        first = 0;
                } else if (counter->attr.exclude_user != eu ||
                           counter->attr.exclude_kernel != ek ||
                           counter->attr.exclude_hv != eh) {
                        return -EAGAIN;
                }
        }

        if (eu || ek || eh)
                for (i = 0; i < n; ++i)
                        if (cflags[i] & PPMU_LIMITED_PMC_OK)
                                cflags[i] |= PPMU_LIMITED_PMC_REQD;

        return 0;
}

static void power_pmu_read(struct perf_counter *counter)
{
        long val, delta, prev;

        if (!counter->hw.idx)
                return;
        /*
         * Performance monitor interrupts come even when interrupts
         * are soft-disabled, as long as interrupts are hard-enabled.
         * Therefore we treat them like NMIs.
         */
        do {
                prev = atomic64_read(&counter->hw.prev_count);
                barrier();
                val = read_pmc(counter->hw.idx);
        } while (atomic64_cmpxchg(&counter->hw.prev_count, prev, val) != prev);

        /* The counters are only 32 bits wide */
        delta = (val - prev) & 0xfffffffful;
        atomic64_add(delta, &counter->count);
        atomic64_sub(delta, &counter->hw.period_left);
}

/*
 * On some machines, PMC5 and PMC6 can't be written, don't respect
 * the freeze conditions, and don't generate interrupts.  This tells
 * us if `counter' is using such a PMC.
 */
static int is_limited_pmc(int pmcnum)
{
        return (ppmu->flags & PPMU_LIMITED_PMC5_6)
                && (pmcnum == 5 || pmcnum == 6);
}

static void freeze_limited_counters(struct cpu_hw_counters *cpuhw,
                                    unsigned long pmc5, unsigned long pmc6)
{
        struct perf_counter *counter;
        u64 val, prev, delta;
        int i;

        for (i = 0; i < cpuhw->n_limited; ++i) {
                counter = cpuhw->limited_counter[i];
                if (!counter->hw.idx)
                        continue;
                val = (counter->hw.idx == 5) ? pmc5 : pmc6;
                prev = atomic64_read(&counter->hw.prev_count);
                counter->hw.idx = 0;
                delta = (val - prev) & 0xfffffffful;
                atomic64_add(delta, &counter->count);
        }
}

static void thaw_limited_counters(struct cpu_hw_counters *cpuhw,
                                  unsigned long pmc5, unsigned long pmc6)
{
        struct perf_counter *counter;
        u64 val;
        int i;

        for (i = 0; i < cpuhw->n_limited; ++i) {
                counter = cpuhw->limited_counter[i];
                counter->hw.idx = cpuhw->limited_hwidx[i];
                val = (counter->hw.idx == 5) ? pmc5 : pmc6;
                atomic64_set(&counter->hw.prev_count, val);
                perf_counter_update_userpage(counter);
        }
}

/*
 * Since limited counters don't respect the freeze conditions, we
 * have to read them immediately after freezing or unfreezing the
 * other counters.  We try to keep the values from the limited
 * counters as consistent as possible by keeping the delay (in
 * cycles and instructions) between freezing/unfreezing and reading
 * the limited counters as small and consistent as possible.
 * Therefore, if any limited counters are in use, we read them
 * both, and always in the same order, to minimize variability,
 * and do it inside the same asm that writes MMCR0.
 */
static void write_mmcr0(struct cpu_hw_counters *cpuhw, unsigned long mmcr0)
{
        unsigned long pmc5, pmc6;

        if (!cpuhw->n_limited) {
                mtspr(SPRN_MMCR0, mmcr0);
                return;
        }

        /*
         * Write MMCR0, then read PMC5 and PMC6 immediately.
         * To ensure we don't get a performance monitor interrupt
         * between writing MMCR0 and freezing/thawing the limited
         * counters, we first write MMCR0 with the counter overflow
         * interrupt enable bits turned off.
         */
        asm volatile("mtspr %3,%2; mfspr %0,%4; mfspr %1,%5"
                     : "=&r" (pmc5), "=&r" (pmc6)
                     : "r" (mmcr0 & ~(MMCR0_PMC1CE | MMCR0_PMCjCE)),
                       "i" (SPRN_MMCR0),
                       "i" (SPRN_PMC5), "i" (SPRN_PMC6));

        if (mmcr0 & MMCR0_FC)
                freeze_limited_counters(cpuhw, pmc5, pmc6);
        else
                thaw_limited_counters(cpuhw, pmc5, pmc6);

        /*
         * Write the full MMCR0 including the counter overflow interrupt
         * enable bits, if necessary.
         */
        if (mmcr0 & (MMCR0_PMC1CE | MMCR0_PMCjCE))
                mtspr(SPRN_MMCR0, mmcr0);
}

/*
 * Disable all counters to prevent PMU interrupts and to allow
 * counters to be added or removed.
 */
void hw_perf_disable(void)
{
        struct cpu_hw_counters *cpuhw;
        unsigned long ret;
        unsigned long flags;

        local_irq_save(flags);
        cpuhw = &__get_cpu_var(cpu_hw_counters);

        ret = cpuhw->disabled;
        if (!ret) {
                cpuhw->disabled = 1;
                cpuhw->n_added = 0;

                /*
                 * Check if we ever enabled the PMU on this cpu.
                 */
                if (!cpuhw->pmcs_enabled) {
                        if (ppc_md.enable_pmcs)
                                ppc_md.enable_pmcs();
                        cpuhw->pmcs_enabled = 1;
                }

                /*
                 * Disable instruction sampling if it was enabled
                 */
                if (cpuhw->mmcr[2] & MMCRA_SAMPLE_ENABLE) {
                        mtspr(SPRN_MMCRA,
                              cpuhw->mmcr[2] & ~MMCRA_SAMPLE_ENABLE);
                        mb();
                }

                /*
                 * Set the 'freeze counters' bit.
                 * The barrier is to make sure the mtspr has been
                 * executed and the PMU has frozen the counters
                 * before we return.
                 */
                write_mmcr0(cpuhw, mfspr(SPRN_MMCR0) | MMCR0_FC);
                mb();
        }
        local_irq_restore(flags);
}

/*
 * Re-enable all counters if disable == 0.
 * If we were previously disabled and counters were added, then
 * put the new config on the PMU.
 */
void hw_perf_enable(void)
{
        struct perf_counter *counter;
        struct cpu_hw_counters *cpuhw;
        unsigned long flags;
        long i;
        unsigned long val;
        s64 left;
        unsigned int hwc_index[MAX_HWCOUNTERS];
        int n_lim;
        int idx;

        local_irq_save(flags);
        cpuhw = &__get_cpu_var(cpu_hw_counters);
        if (!cpuhw->disabled) {
                local_irq_restore(flags);
                return;
        }
        cpuhw->disabled = 0;

        /*
         * If we didn't change anything, or only removed counters,
         * no need to recalculate MMCR* settings and reset the PMCs.
         * Just reenable the PMU with the current MMCR* settings
         * (possibly updated for removal of counters).
         */
        if (!cpuhw->n_added) {
                mtspr(SPRN_MMCRA, cpuhw->mmcr[2] & ~MMCRA_SAMPLE_ENABLE);
                mtspr(SPRN_MMCR1, cpuhw->mmcr[1]);
                if (cpuhw->n_counters == 0)
                        get_lppaca()->pmcregs_in_use = 0;
                goto out_enable;
        }

        /*
         * Compute MMCR* values for the new set of counters
         */
        if (ppmu->compute_mmcr(cpuhw->events, cpuhw->n_counters, hwc_index,
                               cpuhw->mmcr)) {
                /* shouldn't ever get here */
                printk(KERN_ERR "oops compute_mmcr failed\n");
                goto out;
        }

        /*
         * Add in MMCR0 freeze bits corresponding to the
         * attr.exclude_* bits for the first counter.
         * We have already checked that all counters have the
         * same values for these bits as the first counter.
         */
        counter = cpuhw->counter[0];
        if (counter->attr.exclude_user)
                cpuhw->mmcr[0] |= MMCR0_FCP;
        if (counter->attr.exclude_kernel)
                cpuhw->mmcr[0] |= freeze_counters_kernel;
        if (counter->attr.exclude_hv)
                cpuhw->mmcr[0] |= MMCR0_FCHV;

        /*
         * Write the new configuration to MMCR* with the freeze
         * bit set and set the hardware counters to their initial values.
         * Then unfreeze the counters.
         */
        get_lppaca()->pmcregs_in_use = 1;
        mtspr(SPRN_MMCRA, cpuhw->mmcr[2] & ~MMCRA_SAMPLE_ENABLE);
        mtspr(SPRN_MMCR1, cpuhw->mmcr[1]);
        mtspr(SPRN_MMCR0, (cpuhw->mmcr[0] & ~(MMCR0_PMC1CE | MMCR0_PMCjCE))
                                | MMCR0_FC);

        /*
         * Read off any pre-existing counters that need to move
         * to another PMC.
         */
        for (i = 0; i < cpuhw->n_counters; ++i) {
                counter = cpuhw->counter[i];
                if (counter->hw.idx && counter->hw.idx != hwc_index[i] + 1) {
                        power_pmu_read(counter);
                        write_pmc(counter->hw.idx, 0);
                        counter->hw.idx = 0;
                }
        }

        /*
         * Initialize the PMCs for all the new and moved counters.
         */
        cpuhw->n_limited = n_lim = 0;
        for (i = 0; i < cpuhw->n_counters; ++i) {
                counter = cpuhw->counter[i];
                if (counter->hw.idx)
                        continue;
                idx = hwc_index[i] + 1;
                if (is_limited_pmc(idx)) {
                        cpuhw->limited_counter[n_lim] = counter;
                        cpuhw->limited_hwidx[n_lim] = idx;
                        ++n_lim;
                        continue;
                }
                val = 0;
                if (counter->hw.sample_period) {
                        left = atomic64_read(&counter->hw.period_left);
                        if (left < 0x80000000L)
                                val = 0x80000000L - left;
                }
                atomic64_set(&counter->hw.prev_count, val);
                counter->hw.idx = idx;
                write_pmc(idx, val);
                perf_counter_update_userpage(counter);
        }
        cpuhw->n_limited = n_lim;
        cpuhw->mmcr[0] |= MMCR0_PMXE | MMCR0_FCECE;

 out_enable:
        mb();
        write_mmcr0(cpuhw, cpuhw->mmcr[0]);

        /*
         * Enable instruction sampling if necessary
         */
        if (cpuhw->mmcr[2] & MMCRA_SAMPLE_ENABLE) {
                mb();
                mtspr(SPRN_MMCRA, cpuhw->mmcr[2]);
        }

 out:
        local_irq_restore(flags);
}

static int collect_events(struct perf_counter *group, int max_count,
                          struct perf_counter *ctrs[], u64 *events,
                          unsigned int *flags)
{
        int n = 0;
        struct perf_counter *counter;

        if (!is_software_counter(group)) {
                if (n >= max_count)
                        return -1;
                ctrs[n] = group;
                flags[n] = group->hw.counter_base;
                events[n++] = group->hw.config;
        }
        list_for_each_entry(counter, &group->sibling_list, list_entry) {
                if (!is_software_counter(counter) &&
                    counter->state != PERF_COUNTER_STATE_OFF) {
                        if (n >= max_count)
                                return -1;
                        ctrs[n] = counter;
                        flags[n] = counter->hw.counter_base;
                        events[n++] = counter->hw.config;
                }
        }
        return n;
}

static void counter_sched_in(struct perf_counter *counter, int cpu)
{
        counter->state = PERF_COUNTER_STATE_ACTIVE;
        counter->oncpu = cpu;
        counter->tstamp_running += counter->ctx->time - counter->tstamp_stopped;
        if (is_software_counter(counter))
                counter->pmu->enable(counter);
}

/*
 * Called to enable a whole group of counters.
 * Returns 1 if the group was enabled, or -EAGAIN if it could not be.
 * Assumes the caller has disabled interrupts and has
 * frozen the PMU with hw_perf_save_disable.
 */
int hw_perf_group_sched_in(struct perf_counter *group_leader,
               struct perf_cpu_context *cpuctx,
               struct perf_counter_context *ctx, int cpu)
{
        struct cpu_hw_counters *cpuhw;
        long i, n, n0;
        struct perf_counter *sub;

        cpuhw = &__get_cpu_var(cpu_hw_counters);
        n0 = cpuhw->n_counters;
        n = collect_events(group_leader, ppmu->n_counter - n0,
                           &cpuhw->counter[n0], &cpuhw->events[n0],
                           &cpuhw->flags[n0]);
        if (n < 0)
                return -EAGAIN;
        if (check_excludes(cpuhw->counter, cpuhw->flags, n0, n))
                return -EAGAIN;
        i = power_check_constraints(cpuhw->events, cpuhw->flags, n + n0);
        if (i < 0)
                return -EAGAIN;
        cpuhw->n_counters = n0 + n;
        cpuhw->n_added += n;

        /*
         * OK, this group can go on; update counter states etc.,
         * and enable any software counters
         */
        for (i = n0; i < n0 + n; ++i)
                cpuhw->counter[i]->hw.config = cpuhw->events[i];
        cpuctx->active_oncpu += n;
        n = 1;
        counter_sched_in(group_leader, cpu);
        list_for_each_entry(sub, &group_leader->sibling_list, list_entry) {
                if (sub->state != PERF_COUNTER_STATE_OFF) {
                        counter_sched_in(sub, cpu);
                        ++n;
                }
        }
        ctx->nr_active += n;

        return 1;
}

/*
 * Add a counter to the PMU.
 * If all counters are not already frozen, then we disable and
 * re-enable the PMU in order to get hw_perf_enable to do the
 * actual work of reconfiguring the PMU.
 */
static int power_pmu_enable(struct perf_counter *counter)
{
        struct cpu_hw_counters *cpuhw;
        unsigned long flags;
        int n0;
        int ret = -EAGAIN;

        local_irq_save(flags);
        perf_disable();

        /*
         * Add the counter to the list (if there is room)
         * and check whether the total set is still feasible.
         */
        cpuhw = &__get_cpu_var(cpu_hw_counters);
        n0 = cpuhw->n_counters;
        if (n0 >= ppmu->n_counter)
                goto out;
        cpuhw->counter[n0] = counter;
        cpuhw->events[n0] = counter->hw.config;
        cpuhw->flags[n0] = counter->hw.counter_base;
        if (check_excludes(cpuhw->counter, cpuhw->flags, n0, 1))
                goto out;
        if (power_check_constraints(cpuhw->events, cpuhw->flags, n0 + 1))
                goto out;

        counter->hw.config = cpuhw->events[n0];
        ++cpuhw->n_counters;
        ++cpuhw->n_added;

        ret = 0;
 out:
        perf_enable();
        local_irq_restore(flags);
        return ret;
}

/*
 * Remove a counter from the PMU.
 */
static void power_pmu_disable(struct perf_counter *counter)
{
        struct cpu_hw_counters *cpuhw;
        long i;
        unsigned long flags;

        local_irq_save(flags);
        perf_disable();

        power_pmu_read(counter);

        cpuhw = &__get_cpu_var(cpu_hw_counters);
        for (i = 0; i < cpuhw->n_counters; ++i) {
                if (counter == cpuhw->counter[i]) {
                        while (++i < cpuhw->n_counters)
                                cpuhw->counter[i-1] = cpuhw->counter[i];
                        --cpuhw->n_counters;
                        ppmu->disable_pmc(counter->hw.idx - 1, cpuhw->mmcr);
                        if (counter->hw.idx) {
                                write_pmc(counter->hw.idx, 0);
                                counter->hw.idx = 0;
                        }
                        perf_counter_update_userpage(counter);
                        break;
                }
        }
        for (i = 0; i < cpuhw->n_limited; ++i)
                if (counter == cpuhw->limited_counter[i])
                        break;
        if (i < cpuhw->n_limited) {
                while (++i < cpuhw->n_limited) {
                        cpuhw->limited_counter[i-1] = cpuhw->limited_counter[i];
                        cpuhw->limited_hwidx[i-1] = cpuhw->limited_hwidx[i];
                }
                --cpuhw->n_limited;
        }
        if (cpuhw->n_counters == 0) {
                /* disable exceptions if no counters are running */
                cpuhw->mmcr[0] &= ~(MMCR0_PMXE | MMCR0_FCECE);
        }

        perf_enable();
        local_irq_restore(flags);
}

/*
 * Re-enable interrupts on a counter after they were throttled
 * because they were coming too fast.
 */
static void power_pmu_unthrottle(struct perf_counter *counter)
{
        s64 val, left;
        unsigned long flags;

        if (!counter->hw.idx || !counter->hw.sample_period)
                return;
        local_irq_save(flags);
        perf_disable();
        power_pmu_read(counter);
        left = counter->hw.sample_period;
        val = 0;
        if (left < 0x80000000L)
                val = 0x80000000L - left;
        write_pmc(counter->hw.idx, val);
        atomic64_set(&counter->hw.prev_count, val);
        atomic64_set(&counter->hw.period_left, left);
        perf_counter_update_userpage(counter);
        perf_enable();
        local_irq_restore(flags);
}

struct pmu power_pmu = {
        .enable         = power_pmu_enable,
        .disable        = power_pmu_disable,
        .read           = power_pmu_read,
        .unthrottle     = power_pmu_unthrottle,
};

/*
 * Return 1 if we might be able to put counter on a limited PMC,
 * or 0 if not.
 * A counter can only go on a limited PMC if it counts something
 * that a limited PMC can count, doesn't require interrupts, and
 * doesn't exclude any processor mode.
 */
static int can_go_on_limited_pmc(struct perf_counter *counter, u64 ev,
                                 unsigned int flags)
{
        int n;
        u64 alt[MAX_EVENT_ALTERNATIVES];

        if (counter->attr.exclude_user
            || counter->attr.exclude_kernel
            || counter->attr.exclude_hv
            || counter->attr.sample_period)
                return 0;

        if (ppmu->limited_pmc_event(ev))
                return 1;

        /*
         * The requested event isn't on a limited PMC already;
         * see if any alternative code goes on a limited PMC.
         */
        if (!ppmu->get_alternatives)
                return 0;

        flags |= PPMU_LIMITED_PMC_OK | PPMU_LIMITED_PMC_REQD;
        n = ppmu->get_alternatives(ev, flags, alt);

        return n > 0;
}

/*
 * Find an alternative event that goes on a normal PMC, if possible,
 * and return the event code, or 0 if there is no such alternative.
 * (Note: event code 0 is "don't count" on all machines.)
 */
static u64 normal_pmc_alternative(u64 ev, unsigned long flags)
{
        u64 alt[MAX_EVENT_ALTERNATIVES];
        int n;

        flags &= ~(PPMU_LIMITED_PMC_OK | PPMU_LIMITED_PMC_REQD);
        n = ppmu->get_alternatives(ev, flags, alt);
        if (!n)
                return 0;
        return alt[0];
}

/* Number of perf_counters counting hardware events */
static atomic_t num_counters;
/* Used to avoid races in calling reserve/release_pmc_hardware */
static DEFINE_MUTEX(pmc_reserve_mutex);

/*
 * Release the PMU if this is the last perf_counter.
 */
static void hw_perf_counter_destroy(struct perf_counter *counter)
{
        if (!atomic_add_unless(&num_counters, -1, 1)) {
                mutex_lock(&pmc_reserve_mutex);
                if (atomic_dec_return(&num_counters) == 0)
                        release_pmc_hardware();
                mutex_unlock(&pmc_reserve_mutex);
        }
}

const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
{
        u64 ev;
        unsigned long flags;
        struct perf_counter *ctrs[MAX_HWCOUNTERS];
        u64 events[MAX_HWCOUNTERS];
        unsigned int cflags[MAX_HWCOUNTERS];
        int n;
        int err;

        if (!ppmu)
                return ERR_PTR(-ENXIO);
        if (counter->attr.type != PERF_TYPE_RAW) {
                ev = counter->attr.config;
                if (ev >= ppmu->n_generic || ppmu->generic_events[ev] == 0)
                        return ERR_PTR(-EOPNOTSUPP);
                ev = ppmu->generic_events[ev];
        } else {
                ev = counter->attr.config;
        }
        counter->hw.config_base = ev;
        counter->hw.idx = 0;

        /*
         * If we are not running on a hypervisor, force the
         * exclude_hv bit to 0 so that we don't care what
         * the user set it to.
         */
        if (!firmware_has_feature(FW_FEATURE_LPAR))
                counter->attr.exclude_hv = 0;

        /*
         * If this is a per-task counter, then we can use
         * PM_RUN_* events interchangeably with their non RUN_*
         * equivalents, e.g. PM_RUN_CYC instead of PM_CYC.
         * XXX we should check if the task is an idle task.
         */
        flags = 0;
        if (counter->ctx->task)
                flags |= PPMU_ONLY_COUNT_RUN;

        /*
         * If this machine has limited counters, check whether this
         * event could go on a limited counter.
         */
        if (ppmu->flags & PPMU_LIMITED_PMC5_6) {
                if (can_go_on_limited_pmc(counter, ev, flags)) {
                        flags |= PPMU_LIMITED_PMC_OK;
                } else if (ppmu->limited_pmc_event(ev)) {
                        /*
                         * The requested event is on a limited PMC,
                         * but we can't use a limited PMC; see if any
                         * alternative goes on a normal PMC.
                         */
                        ev = normal_pmc_alternative(ev, flags);
                        if (!ev)
                                return ERR_PTR(-EINVAL);
                }
        }

        /*
         * If this is in a group, check if it can go on with all the
         * other hardware counters in the group.  We assume the counter
         * hasn't been linked into its leader's sibling list at this point.
         */
        n = 0;
        if (counter->group_leader != counter) {
                n = collect_events(counter->group_leader, ppmu->n_counter - 1,
                                   ctrs, events, cflags);
                if (n < 0)
                        return ERR_PTR(-EINVAL);
        }
        events[n] = ev;
        ctrs[n] = counter;
        cflags[n] = flags;
        if (check_excludes(ctrs, cflags, n, 1))
                return ERR_PTR(-EINVAL);
        if (power_check_constraints(events, cflags, n + 1))
                return ERR_PTR(-EINVAL);

        counter->hw.config = events[n];
        counter->hw.counter_base = cflags[n];
        atomic64_set(&counter->hw.period_left, counter->hw.sample_period);

        /*
         * See if we need to reserve the PMU.
         * If no counters are currently in use, then we have to take a
         * mutex to ensure that we don't race with another task doing
         * reserve_pmc_hardware or release_pmc_hardware.
         */
        err = 0;
        if (!atomic_inc_not_zero(&num_counters)) {
                mutex_lock(&pmc_reserve_mutex);
                if (atomic_read(&num_counters) == 0 &&
                    reserve_pmc_hardware(perf_counter_interrupt))
                        err = -EBUSY;
                else
                        atomic_inc(&num_counters);
                mutex_unlock(&pmc_reserve_mutex);
        }
        counter->destroy = hw_perf_counter_destroy;

        if (err)
                return ERR_PTR(err);
        return &power_pmu;
}

/*
 * A counter has overflowed; update its count and record
 * things if requested.  Note that interrupts are hard-disabled
 * here so there is no possibility of being interrupted.
 */
static void record_and_restart(struct perf_counter *counter, long val,
                               struct pt_regs *regs, int nmi)
{
        u64 period = counter->hw.sample_period;
        s64 prev, delta, left;
        int record = 0;
        u64 addr, mmcra, sdsync;

        /* we don't have to worry about interrupts here */
        prev = atomic64_read(&counter->hw.prev_count);
        delta = (val - prev) & 0xfffffffful;
        atomic64_add(delta, &counter->count);

        /*
         * See if the total period for this counter has expired,
         * and update for the next period.
         */
        val = 0;
        left = atomic64_read(&counter->hw.period_left) - delta;
        if (period) {
                if (left <= 0) {
                        left += period;
                        if (left <= 0)
                                left = period;
                        record = 1;
                }
                if (left < 0x80000000L)
                        val = 0x80000000L - left;
        }

        /*
         * Finally record data if requested.
         */
        if (record) {
                addr = 0;
                if (counter->attr.sample_type & PERF_SAMPLE_ADDR) {
                        /*
                         * The user wants a data address recorded.
                         * If we're not doing instruction sampling,
                         * give them the SDAR (sampled data address).
                         * If we are doing instruction sampling, then only
                         * give them the SDAR if it corresponds to the
                         * instruction pointed to by SIAR; this is indicated
                         * by the [POWER6_]MMCRA_SDSYNC bit in MMCRA.
                         */
                        mmcra = regs->dsisr;
                        sdsync = (ppmu->flags & PPMU_ALT_SIPR) ?
                                POWER6_MMCRA_SDSYNC : MMCRA_SDSYNC;
                        if (!(mmcra & MMCRA_SAMPLE_ENABLE) || (mmcra & sdsync))
                                addr = mfspr(SPRN_SDAR);
                }
                if (perf_counter_overflow(counter, nmi, regs, addr)) {
                        /*
                         * Interrupts are coming too fast - throttle them
                         * by setting the counter to 0, so it will be
                         * at least 2^30 cycles until the next interrupt
                         * (assuming each counter counts at most 2 counts
                         * per cycle).
                         */
                        val = 0;
                        left = ~0ULL >> 1;
                }
        }

        write_pmc(counter->hw.idx, val);
        atomic64_set(&counter->hw.prev_count, val);
        atomic64_set(&counter->hw.period_left, left);
        perf_counter_update_userpage(counter);
}

/*
 * Called from generic code to get the misc flags (i.e. processor mode)
 * for an event.
 */
unsigned long perf_misc_flags(struct pt_regs *regs)
{
        unsigned long mmcra;

        if (TRAP(regs) != 0xf00) {
                /* not a PMU interrupt */
                return user_mode(regs) ? PERF_EVENT_MISC_USER :
                        PERF_EVENT_MISC_KERNEL;
        }

        mmcra = regs->dsisr;
        if (ppmu->flags & PPMU_ALT_SIPR) {
                if (mmcra & POWER6_MMCRA_SIHV)
                        return PERF_EVENT_MISC_HYPERVISOR;
                return (mmcra & POWER6_MMCRA_SIPR) ? PERF_EVENT_MISC_USER :
                        PERF_EVENT_MISC_KERNEL;
        }
        if (mmcra & MMCRA_SIHV)
                return PERF_EVENT_MISC_HYPERVISOR;
        return (mmcra & MMCRA_SIPR) ? PERF_EVENT_MISC_USER :
                        PERF_EVENT_MISC_KERNEL;
}

/*
 * Called from generic code to get the instruction pointer
 * for an event.
 */
unsigned long perf_instruction_pointer(struct pt_regs *regs)
{
        unsigned long mmcra;
        unsigned long ip;
        unsigned long slot;

        if (TRAP(regs) != 0xf00)
                return regs->nip;       /* not a PMU interrupt */

        ip = mfspr(SPRN_SIAR);
        mmcra = regs->dsisr;
        if ((mmcra & MMCRA_SAMPLE_ENABLE) && !(ppmu->flags & PPMU_ALT_SIPR)) {
                slot = (mmcra & MMCRA_SLOT) >> MMCRA_SLOT_SHIFT;
                if (slot > 1)
                        ip += 4 * (slot - 1);
        }
        return ip;
}

/*
 * Performance monitor interrupt stuff
 */
static void perf_counter_interrupt(struct pt_regs *regs)
{
        int i;
        struct cpu_hw_counters *cpuhw = &__get_cpu_var(cpu_hw_counters);
        struct perf_counter *counter;
        long val;
        int found = 0;
        int nmi;

        if (cpuhw->n_limited)
                freeze_limited_counters(cpuhw, mfspr(SPRN_PMC5),
                                        mfspr(SPRN_PMC6));

        /*
         * Overload regs->dsisr to store MMCRA so we only need to read it once.
         */
        regs->dsisr = mfspr(SPRN_MMCRA);

        /*
         * If interrupts were soft-disabled when this PMU interrupt
         * occurred, treat it as an NMI.
         */
        nmi = !regs->softe;
        if (nmi)
                nmi_enter();
        else
                irq_enter();

        for (i = 0; i < cpuhw->n_counters; ++i) {
                counter = cpuhw->counter[i];
                if (!counter->hw.idx || is_limited_pmc(counter->hw.idx))
                        continue;
                val = read_pmc(counter->hw.idx);
                if ((int)val < 0) {
                        /* counter has overflowed */
                        found = 1;
                        record_and_restart(counter, val, regs, nmi);
                }
        }

        /*
         * In case we didn't find and reset the counter that caused
         * the interrupt, scan all counters and reset any that are
         * negative, to avoid getting continual interrupts.
         * Any that we processed in the previous loop will not be negative.
         */
        if (!found) {
                for (i = 0; i < ppmu->n_counter; ++i) {
                        if (is_limited_pmc(i + 1))
                                continue;
                        val = read_pmc(i + 1);
                        if ((int)val < 0)
                                write_pmc(i + 1, 0);
                }
        }

        /*
         * Reset MMCR0 to its normal value.  This will set PMXE and
         * clear FC (freeze counters) and PMAO (perf mon alert occurred)
         * and thus allow interrupts to occur again.
         * XXX might want to use MSR.PM to keep the counters frozen until
         * we get back out of this interrupt.
         */
        write_mmcr0(cpuhw, cpuhw->mmcr[0]);

        if (nmi)
                nmi_exit();
        else
                irq_exit();
}

void hw_perf_counter_setup(int cpu)
{
        struct cpu_hw_counters *cpuhw = &per_cpu(cpu_hw_counters, cpu);

        memset(cpuhw, 0, sizeof(*cpuhw));
        cpuhw->mmcr[0] = MMCR0_FC;
}

extern struct power_pmu power4_pmu;
extern struct power_pmu ppc970_pmu;
extern struct power_pmu power5_pmu;
extern struct power_pmu power5p_pmu;
extern struct power_pmu power6_pmu;

static int init_perf_counters(void)
{
        unsigned long pvr;

        /* XXX should get this from cputable */
        pvr = mfspr(SPRN_PVR);
        switch (PVR_VER(pvr)) {
        case PV_POWER4:
        case PV_POWER4p:
                ppmu = &power4_pmu;
                break;
        case PV_970:
        case PV_970FX:
        case PV_970MP:
                ppmu = &ppc970_pmu;
                break;
        case PV_POWER5:
                ppmu = &power5_pmu;
                break;
        case PV_POWER5p:
                ppmu = &power5p_pmu;
                break;
        case 0x3e:
                ppmu = &power6_pmu;
                break;
        }

        /*
         * Use FCHV to ignore kernel events if MSR.HV is set.
         */
        if (mfmsr() & MSR_HV)
                freeze_counters_kernel = MMCR0_FCHV;

        return 0;
}

arch_initcall(init_perf_counters);