[MIPS] SMTC: Close tiny holes in the SMTC IPI replay system.

[deliverable/linux.git] / arch / mips / kernel / smtc.c

/* Copyright (C) 2004 Mips Technologies, Inc */

#include <linux/clockchips.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/cpumask.h>
#include <linux/interrupt.h>
#include <linux/kernel_stat.h>
#include <linux/module.h>

#include <asm/cpu.h>
#include <asm/processor.h>
#include <asm/atomic.h>
#include <asm/system.h>
#include <asm/hardirq.h>
#include <asm/hazards.h>
#include <asm/irq.h>
#include <asm/mmu_context.h>
#include <asm/mipsregs.h>
#include <asm/cacheflush.h>
#include <asm/time.h>
#include <asm/addrspace.h>
#include <asm/smtc.h>
#include <asm/smtc_ipi.h>
#include <asm/smtc_proc.h>

/*
 * SMTC Kernel needs to manipulate low-level CPU interrupt mask
 * in do_IRQ. These are passed in setup_irq_smtc() and stored
 * in this table.
 */
unsigned long irq_hwmask[NR_IRQS];

#define LOCK_MT_PRA() \
        local_irq_save(flags); \
        mtflags = dmt()

#define UNLOCK_MT_PRA() \
        emt(mtflags); \
        local_irq_restore(flags)

#define LOCK_CORE_PRA() \
        local_irq_save(flags); \
        mtflags = dvpe()

#define UNLOCK_CORE_PRA() \
        evpe(mtflags); \
        local_irq_restore(flags)

/*
 * Data structures purely associated with SMTC parallelism
 */


/*
 * Table for tracking ASIDs whose lifetime is prolonged.
 */

asiduse smtc_live_asid[MAX_SMTC_TLBS][MAX_SMTC_ASIDS];

/*
 * Clock interrupt "latch" buffers, per "CPU"
 */

static atomic_t ipi_timer_latch[NR_CPUS];

/*
 * Number of InterProcessor Interrupt (IPI) message buffers to allocate
 */

#define IPIBUF_PER_CPU 4

struct smtc_ipi_q IPIQ[NR_CPUS];
static struct smtc_ipi_q freeIPIq;


/* Forward declarations */

void ipi_decode(struct smtc_ipi *);
static void post_direct_ipi(int cpu, struct smtc_ipi *pipi);
static void setup_cross_vpe_interrupts(unsigned int nvpe);
void init_smtc_stats(void);

/* Global SMTC Status */

unsigned int smtc_status = 0;

/* Boot command line configuration overrides */

static int vpe0limit;
static int ipibuffers = 0;
static int nostlb = 0;
static int asidmask = 0;
unsigned long smtc_asid_mask = 0xff;

static int __init vpe0tcs(char *str)
{
        get_option(&str, &vpe0limit);

        return 1;
}

static int __init ipibufs(char *str)
{
        get_option(&str, &ipibuffers);
        return 1;
}

static int __init stlb_disable(char *s)
{
        nostlb = 1;
        return 1;
}

static int __init asidmask_set(char *str)
{
        get_option(&str, &asidmask);
        switch (asidmask) {
        case 0x1:
        case 0x3:
        case 0x7:
        case 0xf:
        case 0x1f:
        case 0x3f:
        case 0x7f:
        case 0xff:
                smtc_asid_mask = (unsigned long)asidmask;
                break;
        default:
                printk("ILLEGAL ASID mask 0x%x from command line\n", asidmask);
        }
        return 1;
}

__setup("vpe0tcs=", vpe0tcs);
__setup("ipibufs=", ipibufs);
__setup("nostlb", stlb_disable);
__setup("asidmask=", asidmask_set);

#ifdef CONFIG_SMTC_IDLE_HOOK_DEBUG

static int hang_trig = 0;

static int __init hangtrig_enable(char *s)
{
        hang_trig = 1;
        return 1;
}


__setup("hangtrig", hangtrig_enable);

#define DEFAULT_BLOCKED_IPI_LIMIT 32

static int timerq_limit = DEFAULT_BLOCKED_IPI_LIMIT;

static int __init tintq(char *str)
{
        get_option(&str, &timerq_limit);
        return 1;
}

__setup("tintq=", tintq);

static int imstuckcount[2][8];
/* vpemask represents IM/IE bits of per-VPE Status registers, low-to-high */
static int vpemask[2][8] = {
        {0, 0, 1, 0, 0, 0, 0, 1},
        {0, 0, 0, 0, 0, 0, 0, 1}
};
int tcnoprog[NR_CPUS];
static atomic_t idle_hook_initialized = {0};
static int clock_hang_reported[NR_CPUS];

#endif /* CONFIG_SMTC_IDLE_HOOK_DEBUG */

/*
 * Configure shared TLB - VPC configuration bit must be set by caller
 */

static void smtc_configure_tlb(void)
{
        int i, tlbsiz, vpes;
        unsigned long mvpconf0;
        unsigned long config1val;

        /* Set up ASID preservation table */
        for (vpes=0; vpes<MAX_SMTC_TLBS; vpes++) {
            for(i = 0; i < MAX_SMTC_ASIDS; i++) {
                smtc_live_asid[vpes][i] = 0;
            }
        }
        mvpconf0 = read_c0_mvpconf0();

        if ((vpes = ((mvpconf0 & MVPCONF0_PVPE)
                        >> MVPCONF0_PVPE_SHIFT) + 1) > 1) {
            /* If we have multiple VPEs, try to share the TLB */
            if ((mvpconf0 & MVPCONF0_TLBS) && !nostlb) {
                /*
                 * If TLB sizing is programmable, shared TLB
                 * size is the total available complement.
                 * Otherwise, we have to take the sum of all
                 * static VPE TLB entries.
                 */
                if ((tlbsiz = ((mvpconf0 & MVPCONF0_PTLBE)
                                >> MVPCONF0_PTLBE_SHIFT)) == 0) {
                    /*
                     * If there's more than one VPE, there had better
                     * be more than one TC, because we need one to bind
                     * to each VPE in turn to be able to read
                     * its configuration state!
                     */
                    settc(1);
                    /* Stop the TC from doing anything foolish */
                    write_tc_c0_tchalt(TCHALT_H);
                    mips_ihb();
                    /* No need to un-Halt - that happens later anyway */
                    for (i=0; i < vpes; i++) {
                        write_tc_c0_tcbind(i);
                        /*
                         * To be 100% sure we're really getting the right
                         * information, we exit the configuration state
                         * and do an IHB after each rebinding.
                         */
                        write_c0_mvpcontrol(
                                read_c0_mvpcontrol() & ~ MVPCONTROL_VPC );
                        mips_ihb();
                        /*
                         * Only count if the MMU Type indicated is TLB
                         */
                        if (((read_vpe_c0_config() & MIPS_CONF_MT) >> 7) == 1) {
                                config1val = read_vpe_c0_config1();
                                tlbsiz += ((config1val >> 25) & 0x3f) + 1;
                        }

                        /* Put core back in configuration state */
                        write_c0_mvpcontrol(
                                read_c0_mvpcontrol() | MVPCONTROL_VPC );
                        mips_ihb();
                    }
                }
                write_c0_mvpcontrol(read_c0_mvpcontrol() | MVPCONTROL_STLB);
                ehb();

                /*
                 * Setup kernel data structures to use software total,
                 * rather than read the per-VPE Config1 value. The values
                 * for "CPU 0" gets copied to all the other CPUs as part
                 * of their initialization in smtc_cpu_setup().
                 */

                /* MIPS32 limits TLB indices to 64 */
                if (tlbsiz > 64)
                        tlbsiz = 64;
                cpu_data[0].tlbsize = current_cpu_data.tlbsize = tlbsiz;
                smtc_status |= SMTC_TLB_SHARED;
                local_flush_tlb_all();

                printk("TLB of %d entry pairs shared by %d VPEs\n",
                        tlbsiz, vpes);
            } else {
                printk("WARNING: TLB Not Sharable on SMTC Boot!\n");
            }
        }
}


/*
 * Incrementally build the CPU map out of constituent MIPS MT cores,
 * using the specified available VPEs and TCs.  Plaform code needs
 * to ensure that each MIPS MT core invokes this routine on reset,
 * one at a time(!).
 *
 * This version of the build_cpu_map and prepare_cpus routines assumes
 * that *all* TCs of a MIPS MT core will be used for Linux, and that
 * they will be spread across *all* available VPEs (to minimise the
 * loss of efficiency due to exception service serialization).
 * An improved version would pick up configuration information and
 * possibly leave some TCs/VPEs as "slave" processors.
 *
 * Use c0_MVPConf0 to find out how many TCs are available, setting up
 * phys_cpu_present_map and the logical/physical mappings.
 */

int __init mipsmt_build_cpu_map(int start_cpu_slot)
{
        int i, ntcs;

        /*
         * The CPU map isn't actually used for anything at this point,
         * so it's not clear what else we should do apart from set
         * everything up so that "logical" = "physical".
         */
        ntcs = ((read_c0_mvpconf0() & MVPCONF0_PTC) >> MVPCONF0_PTC_SHIFT) + 1;
        for (i=start_cpu_slot; i<NR_CPUS && i<ntcs; i++) {
                cpu_set(i, phys_cpu_present_map);
                __cpu_number_map[i] = i;
                __cpu_logical_map[i] = i;
        }
#ifdef CONFIG_MIPS_MT_FPAFF
        /* Initialize map of CPUs with FPUs */
        cpus_clear(mt_fpu_cpumask);
#endif

        /* One of those TC's is the one booting, and not a secondary... */
        printk("%i available secondary CPU TC(s)\n", i - 1);

        return i;
}

/*
 * Common setup before any secondaries are started
 * Make sure all CPU's are in a sensible state before we boot any of the
 * secondaries.
 *
 * For MIPS MT "SMTC" operation, we set up all TCs, spread as evenly
 * as possible across the available VPEs.
 */

static void smtc_tc_setup(int vpe, int tc, int cpu)
{
        settc(tc);
        write_tc_c0_tchalt(TCHALT_H);
        mips_ihb();
        write_tc_c0_tcstatus((read_tc_c0_tcstatus()
                        & ~(TCSTATUS_TKSU | TCSTATUS_DA | TCSTATUS_IXMT))
                        | TCSTATUS_A);
        write_tc_c0_tccontext(0);
        /* Bind tc to vpe */
        write_tc_c0_tcbind(vpe);
        /* In general, all TCs should have the same cpu_data indications */
        memcpy(&cpu_data[cpu], &cpu_data[0], sizeof(struct cpuinfo_mips));
        /* For 34Kf, start with TC/CPU 0 as sole owner of single FPU context */
        if (cpu_data[0].cputype == CPU_34K ||
            cpu_data[0].cputype == CPU_1004K)
                cpu_data[cpu].options &= ~MIPS_CPU_FPU;
        cpu_data[cpu].vpe_id = vpe;
        cpu_data[cpu].tc_id = tc;
}


void mipsmt_prepare_cpus(void)
{
        int i, vpe, tc, ntc, nvpe, tcpervpe[NR_CPUS], slop, cpu;
        unsigned long flags;
        unsigned long val;
        int nipi;
        struct smtc_ipi *pipi;

        /* disable interrupts so we can disable MT */
        local_irq_save(flags);
        /* disable MT so we can configure */
        dvpe();
        dmt();

        spin_lock_init(&freeIPIq.lock);

        /*
         * We probably don't have as many VPEs as we do SMP "CPUs",
         * but it's possible - and in any case we'll never use more!
         */
        for (i=0; i<NR_CPUS; i++) {
                IPIQ[i].head = IPIQ[i].tail = NULL;
                spin_lock_init(&IPIQ[i].lock);
                IPIQ[i].depth = 0;
                atomic_set(&ipi_timer_latch[i], 0);
        }

        /* cpu_data index starts at zero */
        cpu = 0;
        cpu_data[cpu].vpe_id = 0;
        cpu_data[cpu].tc_id = 0;
        cpu++;

        /* Report on boot-time options */
        mips_mt_set_cpuoptions();
        if (vpelimit > 0)
                printk("Limit of %d VPEs set\n", vpelimit);
        if (tclimit > 0)
                printk("Limit of %d TCs set\n", tclimit);
        if (nostlb) {
                printk("Shared TLB Use Inhibited - UNSAFE for Multi-VPE Operation\n");
        }
        if (asidmask)
                printk("ASID mask value override to 0x%x\n", asidmask);

        /* Temporary */
#ifdef CONFIG_SMTC_IDLE_HOOK_DEBUG
        if (hang_trig)
                printk("Logic Analyser Trigger on suspected TC hang\n");
#endif /* CONFIG_SMTC_IDLE_HOOK_DEBUG */

        /* Put MVPE's into 'configuration state' */
        write_c0_mvpcontrol( read_c0_mvpcontrol() | MVPCONTROL_VPC );

        val = read_c0_mvpconf0();
        nvpe = ((val & MVPCONF0_PVPE) >> MVPCONF0_PVPE_SHIFT) + 1;
        if (vpelimit > 0 && nvpe > vpelimit)
                nvpe = vpelimit;
        ntc = ((val & MVPCONF0_PTC) >> MVPCONF0_PTC_SHIFT) + 1;
        if (ntc > NR_CPUS)
                ntc = NR_CPUS;
        if (tclimit > 0 && ntc > tclimit)
                ntc = tclimit;
        slop = ntc % nvpe;
        for (i = 0; i < nvpe; i++) {
                tcpervpe[i] = ntc / nvpe;
                if (slop) {
                        if((slop - i) > 0) tcpervpe[i]++;
                }
        }
        /* Handle command line override for VPE0 */
        if (vpe0limit > ntc) vpe0limit = ntc;
        if (vpe0limit > 0) {
                int slopslop;
                if (vpe0limit < tcpervpe[0]) {
                    /* Reducing TC count - distribute to others */
                    slop = tcpervpe[0] - vpe0limit;
                    slopslop = slop % (nvpe - 1);
                    tcpervpe[0] = vpe0limit;
                    for (i = 1; i < nvpe; i++) {
                        tcpervpe[i] += slop / (nvpe - 1);
                        if(slopslop && ((slopslop - (i - 1) > 0)))
                                tcpervpe[i]++;
                    }
                } else if (vpe0limit > tcpervpe[0]) {
                    /* Increasing TC count - steal from others */
                    slop = vpe0limit - tcpervpe[0];
                    slopslop = slop % (nvpe - 1);
                    tcpervpe[0] = vpe0limit;
                    for (i = 1; i < nvpe; i++) {
                        tcpervpe[i] -= slop / (nvpe - 1);
                        if(slopslop && ((slopslop - (i - 1) > 0)))
                                tcpervpe[i]--;
                    }
                }
        }

        /* Set up shared TLB */
        smtc_configure_tlb();

        for (tc = 0, vpe = 0 ; (vpe < nvpe) && (tc < ntc) ; vpe++) {
                /*
                 * Set the MVP bits.
                 */
                settc(tc);
                write_vpe_c0_vpeconf0(read_vpe_c0_vpeconf0() | VPECONF0_MVP);
                if (vpe != 0)
                        printk(", ");
                printk("VPE %d: TC", vpe);
                for (i = 0; i < tcpervpe[vpe]; i++) {
                        /*
                         * TC 0 is bound to VPE 0 at reset,
                         * and is presumably executing this
                         * code.  Leave it alone!
                         */
                        if (tc != 0) {
                                smtc_tc_setup(vpe, tc, cpu);
                                cpu++;
                        }
                        printk(" %d", tc);
                        tc++;
                }
                if (vpe != 0) {
                        /*
                         * Clear any stale software interrupts from VPE's Cause
                         */
                        write_vpe_c0_cause(0);

                        /*
                         * Clear ERL/EXL of VPEs other than 0
                         * and set restricted interrupt enable/mask.
                         */
                        write_vpe_c0_status((read_vpe_c0_status()
                                & ~(ST0_BEV | ST0_ERL | ST0_EXL | ST0_IM))
                                | (STATUSF_IP0 | STATUSF_IP1 | STATUSF_IP7
                                | ST0_IE));
                        /*
                         * set config to be the same as vpe0,
                         *  particularly kseg0 coherency alg
                         */
                        write_vpe_c0_config(read_c0_config());
                        /* Clear any pending timer interrupt */
                        write_vpe_c0_compare(0);
                        /* Propagate Config7 */
                        write_vpe_c0_config7(read_c0_config7());
                        write_vpe_c0_count(read_c0_count());
                }
                /* enable multi-threading within VPE */
                write_vpe_c0_vpecontrol(read_vpe_c0_vpecontrol() | VPECONTROL_TE);
                /* enable the VPE */
                write_vpe_c0_vpeconf0(read_vpe_c0_vpeconf0() | VPECONF0_VPA);
        }

        /*
         * Pull any physically present but unused TCs out of circulation.
         */
        while (tc < (((val & MVPCONF0_PTC) >> MVPCONF0_PTC_SHIFT) + 1)) {
                cpu_clear(tc, phys_cpu_present_map);
                cpu_clear(tc, cpu_present_map);
                tc++;
        }

        /* release config state */
        write_c0_mvpcontrol( read_c0_mvpcontrol() & ~ MVPCONTROL_VPC );

        printk("\n");

        /* Set up coprocessor affinity CPU mask(s) */

#ifdef CONFIG_MIPS_MT_FPAFF
        for (tc = 0; tc < ntc; tc++) {
                if (cpu_data[tc].options & MIPS_CPU_FPU)
                        cpu_set(tc, mt_fpu_cpumask);
        }
#endif

        /* set up ipi interrupts... */

        /* If we have multiple VPEs running, set up the cross-VPE interrupt */

        setup_cross_vpe_interrupts(nvpe);

        /* Set up queue of free IPI "messages". */
        nipi = NR_CPUS * IPIBUF_PER_CPU;
        if (ipibuffers > 0)
                nipi = ipibuffers;

        pipi = kmalloc(nipi *sizeof(struct smtc_ipi), GFP_KERNEL);
        if (pipi == NULL)
                panic("kmalloc of IPI message buffers failed\n");
        else
                printk("IPI buffer pool of %d buffers\n", nipi);
        for (i = 0; i < nipi; i++) {
                smtc_ipi_nq(&freeIPIq, pipi);
                pipi++;
        }

        /* Arm multithreading and enable other VPEs - but all TCs are Halted */
        emt(EMT_ENABLE);
        evpe(EVPE_ENABLE);
        local_irq_restore(flags);
        /* Initialize SMTC /proc statistics/diagnostics */
        init_smtc_stats();
}


/*
 * Setup the PC, SP, and GP of a secondary processor and start it
 * running!
 * smp_bootstrap is the place to resume from
 * __KSTK_TOS(idle) is apparently the stack pointer
 * (unsigned long)idle->thread_info the gp
 *
 */
void __cpuinit smtc_boot_secondary(int cpu, struct task_struct *idle)
{
        extern u32 kernelsp[NR_CPUS];
        unsigned long flags;
        int mtflags;

        LOCK_MT_PRA();
        if (cpu_data[cpu].vpe_id != cpu_data[smp_processor_id()].vpe_id) {
                dvpe();
        }
        settc(cpu_data[cpu].tc_id);

        /* pc */
        write_tc_c0_tcrestart((unsigned long)&smp_bootstrap);

        /* stack pointer */
        kernelsp[cpu] = __KSTK_TOS(idle);
        write_tc_gpr_sp(__KSTK_TOS(idle));

        /* global pointer */
        write_tc_gpr_gp((unsigned long)task_thread_info(idle));

        smtc_status |= SMTC_MTC_ACTIVE;
        write_tc_c0_tchalt(0);
        if (cpu_data[cpu].vpe_id != cpu_data[smp_processor_id()].vpe_id) {
                evpe(EVPE_ENABLE);
        }
        UNLOCK_MT_PRA();
}

void smtc_init_secondary(void)
{
        /*
         * Start timer on secondary VPEs if necessary.
         * plat_timer_setup has already have been invoked by init/main
         * on "boot" TC.  Like per_cpu_trap_init() hack, this assumes that
         * SMTC init code assigns TCs consdecutively and in ascending order
         * to across available VPEs.
         */
        if (((read_c0_tcbind() & TCBIND_CURTC) != 0) &&
            ((read_c0_tcbind() & TCBIND_CURVPE)
            != cpu_data[smp_processor_id() - 1].vpe_id)){
                write_c0_compare(read_c0_count() + mips_hpt_frequency/HZ);
        }

        local_irq_enable();
}

void smtc_smp_finish(void)
{
        printk("TC %d going on-line as CPU %d\n",
                cpu_data[smp_processor_id()].tc_id, smp_processor_id());
}

void smtc_cpus_done(void)
{
}

/*
 * Support for SMTC-optimized driver IRQ registration
 */

/*
 * SMTC Kernel needs to manipulate low-level CPU interrupt mask
 * in do_IRQ. These are passed in setup_irq_smtc() and stored
 * in this table.
 */

int setup_irq_smtc(unsigned int irq, struct irqaction * new,
                        unsigned long hwmask)
{
#ifdef CONFIG_SMTC_IDLE_HOOK_DEBUG
        unsigned int vpe = current_cpu_data.vpe_id;

        vpemask[vpe][irq - MIPS_CPU_IRQ_BASE] = 1;
#endif
        irq_hwmask[irq] = hwmask;

        return setup_irq(irq, new);
}

#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
/*
 * Support for IRQ affinity to TCs
 */

void smtc_set_irq_affinity(unsigned int irq, cpumask_t affinity)
{
        /*
         * If a "fast path" cache of quickly decodable affinity state
         * is maintained, this is where it gets done, on a call up
         * from the platform affinity code.
         */
}

void smtc_forward_irq(unsigned int irq)
{
        int target;

        /*
         * OK wise guy, now figure out how to get the IRQ
         * to be serviced on an authorized "CPU".
         *
         * Ideally, to handle the situation where an IRQ has multiple
         * eligible CPUS, we would maintain state per IRQ that would
         * allow a fair distribution of service requests.  Since the
         * expected use model is any-or-only-one, for simplicity
         * and efficiency, we just pick the easiest one to find.
         */

        target = first_cpu(irq_desc[irq].affinity);

        /*
         * We depend on the platform code to have correctly processed
         * IRQ affinity change requests to ensure that the IRQ affinity
         * mask has been purged of bits corresponding to nonexistent and
         * offline "CPUs", and to TCs bound to VPEs other than the VPE
         * connected to the physical interrupt input for the interrupt
         * in question.  Otherwise we have a nasty problem with interrupt
         * mask management.  This is best handled in non-performance-critical
         * platform IRQ affinity setting code,  to minimize interrupt-time
         * checks.
         */

        /* If no one is eligible, service locally */
        if (target >= NR_CPUS) {
                do_IRQ_no_affinity(irq);
                return;
        }

        smtc_send_ipi(target, IRQ_AFFINITY_IPI, irq);
}

#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */

/*
 * IPI model for SMTC is tricky, because interrupts aren't TC-specific.
 * Within a VPE one TC can interrupt another by different approaches.
 * The easiest to get right would probably be to make all TCs except
 * the target IXMT and set a software interrupt, but an IXMT-based
 * scheme requires that a handler must run before a new IPI could
 * be sent, which would break the "broadcast" loops in MIPS MT.
 * A more gonzo approach within a VPE is to halt the TC, extract
 * its Restart, Status, and a couple of GPRs, and program the Restart
 * address to emulate an interrupt.
 *
 * Within a VPE, one can be confident that the target TC isn't in
 * a critical EXL state when halted, since the write to the Halt
 * register could not have issued on the writing thread if the
 * halting thread had EXL set. So k0 and k1 of the target TC
 * can be used by the injection code.  Across VPEs, one can't
 * be certain that the target TC isn't in a critical exception
 * state. So we try a two-step process of sending a software
 * interrupt to the target VPE, which either handles the event
 * itself (if it was the target) or injects the event within
 * the VPE.
 */

static void smtc_ipi_qdump(void)
{
        int i;

        for (i = 0; i < NR_CPUS ;i++) {
                printk("IPIQ[%d]: head = 0x%x, tail = 0x%x, depth = %d\n",
                        i, (unsigned)IPIQ[i].head, (unsigned)IPIQ[i].tail,
                        IPIQ[i].depth);
        }
}

/*
 * The standard atomic.h primitives don't quite do what we want
 * here: We need an atomic add-and-return-previous-value (which
 * could be done with atomic_add_return and a decrement) and an
 * atomic set/zero-and-return-previous-value (which can't really
 * be done with the atomic.h primitives). And since this is
 * MIPS MT, we can assume that we have LL/SC.
 */
static inline int atomic_postincrement(atomic_t *v)
{
        unsigned long result;

        unsigned long temp;

        __asm__ __volatile__(
        "1:     ll      %0, %2                                  \n"
        "       addu    %1, %0, 1                               \n"
        "       sc      %1, %2                                  \n"
        "       beqz    %1, 1b                                  \n"
        __WEAK_LLSC_MB
        : "=&r" (result), "=&r" (temp), "=m" (v->counter)
        : "m" (v->counter)
        : "memory");

        return result;
}

void smtc_send_ipi(int cpu, int type, unsigned int action)
{
        int tcstatus;
        struct smtc_ipi *pipi;
        unsigned long flags;
        int mtflags;

        if (cpu == smp_processor_id()) {
                printk("Cannot Send IPI to self!\n");
                return;
        }
        /* Set up a descriptor, to be delivered either promptly or queued */
        pipi = smtc_ipi_dq(&freeIPIq);
        if (pipi == NULL) {
                bust_spinlocks(1);
                mips_mt_regdump(dvpe());
                panic("IPI Msg. Buffers Depleted\n");
        }
        pipi->type = type;
        pipi->arg = (void *)action;
        pipi->dest = cpu;
        if (cpu_data[cpu].vpe_id != cpu_data[smp_processor_id()].vpe_id) {
                if (type == SMTC_CLOCK_TICK)
                        atomic_inc(&ipi_timer_latch[cpu]);
                /* If not on same VPE, enqueue and send cross-VPE interrupt */
                smtc_ipi_nq(&IPIQ[cpu], pipi);
                LOCK_CORE_PRA();
                settc(cpu_data[cpu].tc_id);
                write_vpe_c0_cause(read_vpe_c0_cause() | C_SW1);
                UNLOCK_CORE_PRA();
        } else {
                /*
                 * Not sufficient to do a LOCK_MT_PRA (dmt) here,
                 * since ASID shootdown on the other VPE may
                 * collide with this operation.
                 */
                LOCK_CORE_PRA();
                settc(cpu_data[cpu].tc_id);
                /* Halt the targeted TC */
                write_tc_c0_tchalt(TCHALT_H);
                mips_ihb();

                /*
                 * Inspect TCStatus - if IXMT is set, we have to queue
                 * a message. Otherwise, we set up the "interrupt"
                 * of the other TC
                 */
                tcstatus = read_tc_c0_tcstatus();

                if ((tcstatus & TCSTATUS_IXMT) != 0) {
                        /*
                         * Spin-waiting here can deadlock,
                         * so we queue the message for the target TC.
                         */
                        write_tc_c0_tchalt(0);
                        UNLOCK_CORE_PRA();
                        /* Try to reduce redundant timer interrupt messages */
                        if (type == SMTC_CLOCK_TICK) {
                            if (atomic_postincrement(&ipi_timer_latch[cpu])!=0){
                                smtc_ipi_nq(&freeIPIq, pipi);
                                return;
                            }
                        }
                        smtc_ipi_nq(&IPIQ[cpu], pipi);
                } else {
                        if (type == SMTC_CLOCK_TICK)
                                atomic_inc(&ipi_timer_latch[cpu]);
                        post_direct_ipi(cpu, pipi);
                        write_tc_c0_tchalt(0);
                        UNLOCK_CORE_PRA();
                }
        }
}

/*
 * Send IPI message to Halted TC, TargTC/TargVPE already having been set
 */
static void post_direct_ipi(int cpu, struct smtc_ipi *pipi)
{
        struct pt_regs *kstack;
        unsigned long tcstatus;
        unsigned long tcrestart;
        extern u32 kernelsp[NR_CPUS];
        extern void __smtc_ipi_vector(void);
//printk("%s: on %d for %d\n", __func__, smp_processor_id(), cpu);

        /* Extract Status, EPC from halted TC */
        tcstatus = read_tc_c0_tcstatus();
        tcrestart = read_tc_c0_tcrestart();
        /* If TCRestart indicates a WAIT instruction, advance the PC */
        if ((tcrestart & 0x80000000)
            && ((*(unsigned int *)tcrestart & 0xfe00003f) == 0x42000020)) {
                tcrestart += 4;
        }
        /*
         * Save on TC's future kernel stack
         *
         * CU bit of Status is indicator that TC was
         * already running on a kernel stack...
         */
        if (tcstatus & ST0_CU0)  {
                /* Note that this "- 1" is pointer arithmetic */
                kstack = ((struct pt_regs *)read_tc_gpr_sp()) - 1;
        } else {
                kstack = ((struct pt_regs *)kernelsp[cpu]) - 1;
        }

        kstack->cp0_epc = (long)tcrestart;
        /* Save TCStatus */
        kstack->cp0_tcstatus = tcstatus;
        /* Pass token of operation to be performed kernel stack pad area */
        kstack->pad0[4] = (unsigned long)pipi;
        /* Pass address of function to be called likewise */
        kstack->pad0[5] = (unsigned long)&ipi_decode;
        /* Set interrupt exempt and kernel mode */
        tcstatus |= TCSTATUS_IXMT;
        tcstatus &= ~TCSTATUS_TKSU;
        write_tc_c0_tcstatus(tcstatus);
        ehb();
        /* Set TC Restart address to be SMTC IPI vector */
        write_tc_c0_tcrestart(__smtc_ipi_vector);
}

static void ipi_resched_interrupt(void)
{
        /* Return from interrupt should be enough to cause scheduler check */
}

static void ipi_call_interrupt(void)
{
        /* Invoke generic function invocation code in smp.c */
        smp_call_function_interrupt();
}

DECLARE_PER_CPU(struct clock_event_device, smtc_dummy_clockevent_device);

void ipi_decode(struct smtc_ipi *pipi)
{
        unsigned int cpu = smp_processor_id();
        struct clock_event_device *cd;
        void *arg_copy = pipi->arg;
        int type_copy = pipi->type;
        int ticks;

        smtc_ipi_nq(&freeIPIq, pipi);
        switch (type_copy) {
        case SMTC_CLOCK_TICK:
                irq_enter();
                kstat_this_cpu.irqs[MIPS_CPU_IRQ_BASE + 1]++;
                cd = &per_cpu(smtc_dummy_clockevent_device, cpu);
                ticks = atomic_read(&ipi_timer_latch[cpu]);
                atomic_sub(ticks, &ipi_timer_latch[cpu]);
                while (ticks) {
                        cd->event_handler(cd);
                        ticks--;
                }
                irq_exit();
                break;

        case LINUX_SMP_IPI:
                switch ((int)arg_copy) {
                case SMP_RESCHEDULE_YOURSELF:
                        ipi_resched_interrupt();
                        break;
                case SMP_CALL_FUNCTION:
                        ipi_call_interrupt();
                        break;
                default:
                        printk("Impossible SMTC IPI Argument 0x%x\n",
                                (int)arg_copy);
                        break;
                }
                break;
#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
        case IRQ_AFFINITY_IPI:
                /*
                 * Accept a "forwarded" interrupt that was initially
                 * taken by a TC who doesn't have affinity for the IRQ.
                 */
                do_IRQ_no_affinity((int)arg_copy);
                break;
#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */
        default:
                printk("Impossible SMTC IPI Type 0x%x\n", type_copy);
                break;
        }
}

void deferred_smtc_ipi(void)
{
        struct smtc_ipi *pipi;
        unsigned long flags;
/* DEBUG */
        int q = smp_processor_id();

        /*
         * Test is not atomic, but much faster than a dequeue,
         * and the vast majority of invocations will have a null queue.
         */
        if (IPIQ[q].head != NULL) {
                while((pipi = smtc_ipi_dq(&IPIQ[q])) != NULL) {
                        /* ipi_decode() should be called with interrupts off */
                        local_irq_save(flags);
                        ipi_decode(pipi);
                        local_irq_restore(flags);
                }
        }
}

/*
 * Cross-VPE interrupts in the SMTC prototype use "software interrupts"
 * set via cross-VPE MTTR manipulation of the Cause register. It would be
 * in some regards preferable to have external logic for "doorbell" hardware
 * interrupts.
 */

static int cpu_ipi_irq = MIPS_CPU_IRQ_BASE + MIPS_CPU_IPI_IRQ;

static irqreturn_t ipi_interrupt(int irq, void *dev_idm)
{
        int my_vpe = cpu_data[smp_processor_id()].vpe_id;
        int my_tc = cpu_data[smp_processor_id()].tc_id;
        int cpu;
        struct smtc_ipi *pipi;
        unsigned long tcstatus;
        int sent;
        unsigned long flags;
        unsigned int mtflags;
        unsigned int vpflags;

        /*
         * So long as cross-VPE interrupts are done via
         * MFTR/MTTR read-modify-writes of Cause, we need
         * to stop other VPEs whenever the local VPE does
         * anything similar.
         */
        local_irq_save(flags);
        vpflags = dvpe();
        clear_c0_cause(0x100 << MIPS_CPU_IPI_IRQ);
        set_c0_status(0x100 << MIPS_CPU_IPI_IRQ);
        irq_enable_hazard();
        evpe(vpflags);
        local_irq_restore(flags);

        /*
         * Cross-VPE Interrupt handler: Try to directly deliver IPIs
         * queued for TCs on this VPE other than the current one.
         * Return-from-interrupt should cause us to drain the queue
         * for the current TC, so we ought not to have to do it explicitly here.
         */

        for_each_online_cpu(cpu) {
                if (cpu_data[cpu].vpe_id != my_vpe)
                        continue;

                pipi = smtc_ipi_dq(&IPIQ[cpu]);
                if (pipi != NULL) {
                        if (cpu_data[cpu].tc_id != my_tc) {
                                sent = 0;
                                LOCK_MT_PRA();
                                settc(cpu_data[cpu].tc_id);
                                write_tc_c0_tchalt(TCHALT_H);
                                mips_ihb();
                                tcstatus = read_tc_c0_tcstatus();
                                if ((tcstatus & TCSTATUS_IXMT) == 0) {
                                        post_direct_ipi(cpu, pipi);
                                        sent = 1;
                                }
                                write_tc_c0_tchalt(0);
                                UNLOCK_MT_PRA();
                                if (!sent) {
                                        smtc_ipi_req(&IPIQ[cpu], pipi);
                                }
                        } else {
                                /*
                                 * ipi_decode() should be called
                                 * with interrupts off
                                 */
                                local_irq_save(flags);
                                ipi_decode(pipi);
                                local_irq_restore(flags);
                        }
                }
        }

        return IRQ_HANDLED;
}

static void ipi_irq_dispatch(void)
{
        do_IRQ(cpu_ipi_irq);
}

static struct irqaction irq_ipi = {
        .handler        = ipi_interrupt,
        .flags          = IRQF_DISABLED,
        .name           = "SMTC_IPI",
        .flags          = IRQF_PERCPU
};

static void setup_cross_vpe_interrupts(unsigned int nvpe)
{
        if (nvpe < 1)
                return;

        if (!cpu_has_vint)
                panic("SMTC Kernel requires Vectored Interrupt support");

        set_vi_handler(MIPS_CPU_IPI_IRQ, ipi_irq_dispatch);

        setup_irq_smtc(cpu_ipi_irq, &irq_ipi, (0x100 << MIPS_CPU_IPI_IRQ));

        set_irq_handler(cpu_ipi_irq, handle_percpu_irq);
}

/*
 * SMTC-specific hacks invoked from elsewhere in the kernel.
 *
 * smtc_ipi_replay is called from raw_local_irq_restore which is only ever
 * called with interrupts disabled.  We do rely on interrupts being disabled
 * here because using spin_lock_irqsave()/spin_unlock_irqrestore() would
 * result in a recursive call to raw_local_irq_restore().
 */

static void __smtc_ipi_replay(void)
{
        unsigned int cpu = smp_processor_id();

        /*
         * To the extent that we've ever turned interrupts off,
         * we may have accumulated deferred IPIs.  This is subtle.
         * If we use the smtc_ipi_qdepth() macro, we'll get an
         * exact number - but we'll also disable interrupts
         * and create a window of failure where a new IPI gets
         * queued after we test the depth but before we re-enable
         * interrupts. So long as IXMT never gets set, however,
         * we should be OK:  If we pick up something and dispatch
         * it here, that's great. If we see nothing, but concurrent
         * with this operation, another TC sends us an IPI, IXMT
         * is clear, and we'll handle it as a real pseudo-interrupt
         * and not a pseudo-pseudo interrupt.
         */
        if (IPIQ[cpu].depth > 0) {
                while (1) {
                        struct smtc_ipi_q *q = &IPIQ[cpu];
                        struct smtc_ipi *pipi;
                        extern void self_ipi(struct smtc_ipi *);

                        spin_lock(&q->lock);
                        pipi = __smtc_ipi_dq(q);
                        spin_unlock(&q->lock);
                        if (!pipi)
                                break;

                        self_ipi(pipi);
                        smtc_cpu_stats[cpu].selfipis++;
                }
        }
}

void smtc_ipi_replay(void)
{
        raw_local_irq_disable();
        __smtc_ipi_replay();
}

EXPORT_SYMBOL(smtc_ipi_replay);

void smtc_idle_loop_hook(void)
{
#ifdef CONFIG_SMTC_IDLE_HOOK_DEBUG
        int im;
        int flags;
        int mtflags;
        int bit;
        int vpe;
        int tc;
        int hook_ntcs;
        /*
         * printk within DMT-protected regions can deadlock,
         * so buffer diagnostic messages for later output.
         */
        char *pdb_msg;
        char id_ho_db_msg[768]; /* worst-case use should be less than 700 */

        if (atomic_read(&idle_hook_initialized) == 0) { /* fast test */
                if (atomic_add_return(1, &idle_hook_initialized) == 1) {
                        int mvpconf0;
                        /* Tedious stuff to just do once */
                        mvpconf0 = read_c0_mvpconf0();
                        hook_ntcs = ((mvpconf0 & MVPCONF0_PTC) >> MVPCONF0_PTC_SHIFT) + 1;
                        if (hook_ntcs > NR_CPUS)
                                hook_ntcs = NR_CPUS;
                        for (tc = 0; tc < hook_ntcs; tc++) {
                                tcnoprog[tc] = 0;
                                clock_hang_reported[tc] = 0;
                        }
                        for (vpe = 0; vpe < 2; vpe++)
                                for (im = 0; im < 8; im++)
                                        imstuckcount[vpe][im] = 0;
                        printk("Idle loop test hook initialized for %d TCs\n", hook_ntcs);
                        atomic_set(&idle_hook_initialized, 1000);
                } else {
                        /* Someone else is initializing in parallel - let 'em finish */
                        while (atomic_read(&idle_hook_initialized) < 1000)
                                ;
                }
        }

        /* Have we stupidly left IXMT set somewhere? */
        if (read_c0_tcstatus() & 0x400) {
                write_c0_tcstatus(read_c0_tcstatus() & ~0x400);
                ehb();
                printk("Dangling IXMT in cpu_idle()\n");
        }

        /* Have we stupidly left an IM bit turned off? */
#define IM_LIMIT 2000
        local_irq_save(flags);
        mtflags = dmt();
        pdb_msg = &id_ho_db_msg[0];
        im = read_c0_status();
        vpe = current_cpu_data.vpe_id;
        for (bit = 0; bit < 8; bit++) {
                /*
                 * In current prototype, I/O interrupts
                 * are masked for VPE > 0
                 */
                if (vpemask[vpe][bit]) {
                        if (!(im & (0x100 << bit)))
                                imstuckcount[vpe][bit]++;
                        else
                                imstuckcount[vpe][bit] = 0;
                        if (imstuckcount[vpe][bit] > IM_LIMIT) {
                                set_c0_status(0x100 << bit);
                                ehb();
                                imstuckcount[vpe][bit] = 0;
                                pdb_msg += sprintf(pdb_msg,
                                        "Dangling IM %d fixed for VPE %d\n", bit,
                                        vpe);
                        }
                }
        }

        /*
         * Now that we limit outstanding timer IPIs, check for hung TC
         */
        for (tc = 0; tc < NR_CPUS; tc++) {
                /* Don't check ourself - we'll dequeue IPIs just below */
                if ((tc != smp_processor_id()) &&
                    atomic_read(&ipi_timer_latch[tc]) > timerq_limit) {
                    if (clock_hang_reported[tc] == 0) {
                        pdb_msg += sprintf(pdb_msg,
                                "TC %d looks hung with timer latch at %d\n",
                                tc, atomic_read(&ipi_timer_latch[tc]));
                        clock_hang_reported[tc]++;
                        }
                }
        }
        emt(mtflags);
        local_irq_restore(flags);
        if (pdb_msg != &id_ho_db_msg[0])
                printk("CPU%d: %s", smp_processor_id(), id_ho_db_msg);
#endif /* CONFIG_SMTC_IDLE_HOOK_DEBUG */

        /*
         * Replay any accumulated deferred IPIs. If "Instant Replay"
         * is in use, there should never be any.
         */
#ifndef CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY
        {
                unsigned long flags;

                local_irq_save(flags);
                __smtc_ipi_replay();
                local_irq_restore(flags);
        }
#endif /* CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY */
}

void smtc_soft_dump(void)
{
        int i;

        printk("Counter Interrupts taken per CPU (TC)\n");
        for (i=0; i < NR_CPUS; i++) {
                printk("%d: %ld\n", i, smtc_cpu_stats[i].timerints);
        }
        printk("Self-IPI invocations:\n");
        for (i=0; i < NR_CPUS; i++) {
                printk("%d: %ld\n", i, smtc_cpu_stats[i].selfipis);
        }
        smtc_ipi_qdump();
        printk("Timer IPI Backlogs:\n");
        for (i=0; i < NR_CPUS; i++) {
                printk("%d: %d\n", i, atomic_read(&ipi_timer_latch[i]));
        }
        printk("%d Recoveries of \"stolen\" FPU\n",
               atomic_read(&smtc_fpu_recoveries));
}


/*
 * TLB management routines special to SMTC
 */

void smtc_get_new_mmu_context(struct mm_struct *mm, unsigned long cpu)
{
        unsigned long flags, mtflags, tcstat, prevhalt, asid;
        int tlb, i;

        /*
         * It would be nice to be able to use a spinlock here,
         * but this is invoked from within TLB flush routines
         * that protect themselves with DVPE, so if a lock is
         * held by another TC, it'll never be freed.
         *
         * DVPE/DMT must not be done with interrupts enabled,
         * so even so most callers will already have disabled
         * them, let's be really careful...
         */

        local_irq_save(flags);
        if (smtc_status & SMTC_TLB_SHARED) {
                mtflags = dvpe();
                tlb = 0;
        } else {
                mtflags = dmt();
                tlb = cpu_data[cpu].vpe_id;
        }
        asid = asid_cache(cpu);

        do {
                if (!((asid += ASID_INC) & ASID_MASK) ) {
                        if (cpu_has_vtag_icache)
                                flush_icache_all();
                        /* Traverse all online CPUs (hack requires contigous range) */
                        for_each_online_cpu(i) {
                                /*
                                 * We don't need to worry about our own CPU, nor those of
                                 * CPUs who don't share our TLB.
                                 */
                                if ((i != smp_processor_id()) &&
                                    ((smtc_status & SMTC_TLB_SHARED) ||
                                     (cpu_data[i].vpe_id == cpu_data[cpu].vpe_id))) {
                                        settc(cpu_data[i].tc_id);
                                        prevhalt = read_tc_c0_tchalt() & TCHALT_H;
                                        if (!prevhalt) {
                                                write_tc_c0_tchalt(TCHALT_H);
                                                mips_ihb();
                                        }
                                        tcstat = read_tc_c0_tcstatus();
                                        smtc_live_asid[tlb][(tcstat & ASID_MASK)] |= (asiduse)(0x1 << i);
                                        if (!prevhalt)
                                                write_tc_c0_tchalt(0);
                                }
                        }
                        if (!asid)              /* fix version if needed */
                                asid = ASID_FIRST_VERSION;
                        local_flush_tlb_all();  /* start new asid cycle */
                }
        } while (smtc_live_asid[tlb][(asid & ASID_MASK)]);

        /*
         * SMTC shares the TLB within VPEs and possibly across all VPEs.
         */
        for_each_online_cpu(i) {
                if ((smtc_status & SMTC_TLB_SHARED) ||
                    (cpu_data[i].vpe_id == cpu_data[cpu].vpe_id))
                        cpu_context(i, mm) = asid_cache(i) = asid;
        }

        if (smtc_status & SMTC_TLB_SHARED)
                evpe(mtflags);
        else
                emt(mtflags);
        local_irq_restore(flags);
}

/*
 * Invoked from macros defined in mmu_context.h
 * which must already have disabled interrupts
 * and done a DVPE or DMT as appropriate.
 */

void smtc_flush_tlb_asid(unsigned long asid)
{
        int entry;
        unsigned long ehi;

        entry = read_c0_wired();

        /* Traverse all non-wired entries */
        while (entry < current_cpu_data.tlbsize) {
                write_c0_index(entry);
                ehb();
                tlb_read();
                ehb();
                ehi = read_c0_entryhi();
                if ((ehi & ASID_MASK) == asid) {
                    /*
                     * Invalidate only entries with specified ASID,
                     * makiing sure all entries differ.
                     */
                    write_c0_entryhi(CKSEG0 + (entry << (PAGE_SHIFT + 1)));
                    write_c0_entrylo0(0);
                    write_c0_entrylo1(0);
                    mtc0_tlbw_hazard();
                    tlb_write_indexed();
                }
                entry++;
        }
        write_c0_index(PARKED_INDEX);
        tlbw_use_hazard();
}

/*
 * Support for single-threading cache flush operations.
 */

static int halt_state_save[NR_CPUS];

/*
 * To really, really be sure that nothing is being done
 * by other TCs, halt them all.  This code assumes that
 * a DVPE has already been done, so while their Halted
 * state is theoretically architecturally unstable, in
 * practice, it's not going to change while we're looking
 * at it.
 */

void smtc_cflush_lockdown(void)
{
        int cpu;

        for_each_online_cpu(cpu) {
                if (cpu != smp_processor_id()) {
                        settc(cpu_data[cpu].tc_id);
                        halt_state_save[cpu] = read_tc_c0_tchalt();
                        write_tc_c0_tchalt(TCHALT_H);
                }
        }
        mips_ihb();
}

/* It would be cheating to change the cpu_online states during a flush! */

void smtc_cflush_release(void)
{
        int cpu;

        /*
         * Start with a hazard barrier to ensure
         * that all CACHE ops have played through.
         */
        mips_ihb();

        for_each_online_cpu(cpu) {
                if (cpu != smp_processor_id()) {
                        settc(cpu_data[cpu].tc_id);
                        write_tc_c0_tchalt(halt_state_save[cpu]);
                }
        }
        mips_ihb();
}