[MIPS] MT: Improved multithreading support.

    
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 1322 insertions, 0 deletions

diff --git a/arch/mips/kernel/smtc.c b/arch/mips/kernel/smtc.c
new file mode 100644
index 000000000000..2e8e52c135e6
--- /dev/null
+++ b/arch/mips/kernel/smtc.c
@@ -0,0 +1,1322 @@
+/* Copyright (C) 2004 Mips Technologies, Inc */
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/cpumask.h>
+#include <linux/interrupt.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/mmu_context.h>
+#include <asm/smp.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>
+
+/*
+ * This file should be built into the kernel only if CONFIG_MIPS_MT_SMTC is set.
+ */
+
+/*
+ * MIPSCPU_INT_BASE is identically defined in both
+ * asm-mips/mips-boards/maltaint.h and asm-mips/mips-boards/simint.h,
+ * but as yet there's no properly organized include structure that
+ * will ensure that the right *int.h file will be included for a
+ * given platform build.
+ */
+
+#define MIPSCPU_INT_BASE        16
+
+#define MIPS_CPU_IPI_IRQ        1
+
+#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"
+ */
+
+unsigned int ipi_timer_latch[NR_CPUS];
+
+/*
+ * Number of InterProcessor Interupt (IPI) message buffers to allocate
+ */
+
+#define IPIBUF_PER_CPU 4
+
+struct smtc_ipi_q IPIQ[NR_CPUS];
+struct smtc_ipi_q freeIPIq;
+
+
+/* Forward declarations */
+
+void ipi_decode(struct pt_regs *, struct smtc_ipi *);
+void post_direct_ipi(int cpu, struct smtc_ipi *pipi);
+void setup_cross_vpe_interrupts(void);
+void init_smtc_stats(void);
+
+/* Global SMTC Status */
+
+unsigned int smtc_status = 0;
+
+/* Boot command line configuration overrides */
+
+static int vpelimit = 0;
+static int tclimit = 0;
+static int ipibuffers = 0;
+static int nostlb = 0;
+static int asidmask = 0;
+unsigned long smtc_asid_mask = 0xff;
+
+static int __init maxvpes(char *str)
+{
+        get_option(&str, &vpelimit);
+        return 1;
+}
+
+static int __init maxtcs(char *str)
+{
+        get_option(&str, &tclimit);
+        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("maxvpes=", maxvpes);
+__setup("maxtcs=", maxtcs);
+__setup("ipibufs=", ipibufs);
+__setup("nostlb", stlb_disable);
+__setup("asidmask=", asidmask_set);
+
+/* Enable additional debug checks before going into CPU idle loop */
+#define SMTC_IDLE_HOOK_DEBUG
+
+#ifdef 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);
+
+int imstuckcount[2][8];
+/* vpemask represents IM/IE bits of per-VPE Status registers, low-to-high */
+int vpemask[2][8] = {{0,1,1,0,0,0,0,1},{0,1,0,0,0,0,0,1}};
+int tcnoprog[NR_CPUS];
+static atomic_t idle_hook_initialized = {0};
+static int clock_hang_reported[NR_CPUS];
+
+#endif /* SMTC_IDLE_HOOK_DEBUG */
+
+/* Initialize shared TLB - the should probably migrate to smtc_setup_cpus() */
+
+void __init sanitize_tlb_entries(void)
+{
+        printk("Deprecated sanitize_tlb_entries() invoked\n");
+}
+
+
+/*
+ * Configure shared TLB - VPC configuration bit must be set by caller
+ */
+
+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);
+
+                /*
+                 * 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().
+                 */
+
+                tlbsiz = tlbsiz & 0x3f; /* MIPS32 limits TLB indices to 64 */
+                cpu_data[0].tlbsize = tlbsiz;
+                smtc_status |= SMTC_TLB_SHARED;
+
+                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;
+        }
+        /* Initialize map of CPUs with FPUs */
+        cpus_clear(mt_fpu_cpumask);
+
+        /* 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[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, 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();
+
+        freeIPIq.lock = SPIN_LOCK_UNLOCKED;
+
+        /*
+         * 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;
+                IPIQ[i].lock = SPIN_LOCK_UNLOCKED;
+                IPIQ[i].depth = 0;
+                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 SMTC_IDLE_HOOK_DEBUG
+        if (hang_trig)
+                printk("Logic Analyser Trigger on suspected TC hang\n");
+#endif /* 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;
+        tcpervpe = ntc / nvpe;
+        slop = ntc % nvpe;      /* Residual TCs, < NVPE */
+
+        /* 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; 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 (slop) {
+                        if (tc != 0) {
+                                smtc_tc_setup(vpe,tc, cpu);
+                                cpu++;
+                        }
+                        printk(" %d", tc);
+                        tc++;
+                        slop--;
+                }
+                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());
+                }
+                /* 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) */
+
+        for (tc = 0; tc < ntc; tc++) {
+                if(cpu_data[tc].options & MIPS_CPU_FPU)
+                        cpu_set(tc, mt_fpu_cpumask);
+        }
+
+        /* set up ipi interrupts... */
+
+        /* If we have multiple VPEs running, set up the cross-VPE interrupt */
+
+        if (nvpe > 1)
+                setup_cross_vpe_interrupts();
+
+        /* 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 smtc_boot_secondary(int cpu, struct task_struct *idle)
+{
+        extern u32 kernelsp[NR_CPUS];
+        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)idle->thread_info);
+
+        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.
+         * mips_timer_setup should 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)
+{
+        irq_hwmask[irq] = hwmask;
+
+        return setup_irq(irq, new);
+}
+
+/*
+ * 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.
+ */
+
+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(unsigned int *pv)
+{
+        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"
+        "       sync                                            \n"
+        : "=&r" (result), "=&r" (temp), "=m" (*pv)
+        : "m" (*pv)
+        : "memory");
+
+        return result;
+}
+
+/* No longer used in IPI dispatch, but retained for future recycling */
+
+static __inline__ int atomic_postclear(unsigned int *pv)
+{
+        unsigned long result;
+
+        unsigned long temp;
+
+        __asm__ __volatile__(
+        "1:     ll      %0, %2                                  \n"
+        "       or      %1, $0, $0                              \n"
+        "       sc      %1, %2                                  \n"
+        "       beqz    %1, 1b                                  \n"
+        "       sync                                            \n"
+        : "=&r" (result), "=&r" (temp), "=m" (*pv)
+        : "m" (*pv)
+        : "memory");
+
+        return result;
+}
+
+
+void smtc_send_ipi(int cpu, int type, unsigned int action)
+{
+        int tcstatus;
+        struct smtc_ipi *pipi;
+        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 not on same VPE, enqueue and send cross-VPE interupt */
+                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 {
+                        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
+ */
+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);
+
+        /* 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);
+}
+
+void ipi_resched_interrupt(struct pt_regs *regs)
+{
+        /* Return from interrupt should be enough to cause scheduler check */
+}
+
+
+void ipi_call_interrupt(struct pt_regs *regs)
+{
+        /* Invoke generic function invocation code in smp.c */
+        smp_call_function_interrupt();
+}
+
+void ipi_decode(struct pt_regs *regs, struct smtc_ipi *pipi)
+{
+        void *arg_copy = pipi->arg;
+        int type_copy = pipi->type;
+        int dest_copy = pipi->dest;
+
+        smtc_ipi_nq(&freeIPIq, pipi);
+        switch (type_copy) {
+                case SMTC_CLOCK_TICK:
+                        /* Invoke Clock "Interrupt" */
+                        ipi_timer_latch[dest_copy] = 0;
+#ifdef SMTC_IDLE_HOOK_DEBUG
+                        clock_hang_reported[dest_copy] = 0;
+#endif /* SMTC_IDLE_HOOK_DEBUG */
+                        local_timer_interrupt(0, NULL, regs);
+                        break;
+                case LINUX_SMP_IPI:
+                        switch ((int)arg_copy) {
+                        case SMP_RESCHEDULE_YOURSELF:
+                                ipi_resched_interrupt(regs);
+                                break;
+                        case SMP_CALL_FUNCTION:
+                                ipi_call_interrupt(regs);
+                                break;
+                        default:
+                                printk("Impossible SMTC IPI Argument 0x%x\n",
+                                        (int)arg_copy);
+                                break;
+                        }
+                        break;
+                default:
+                        printk("Impossible SMTC IPI Type 0x%x\n", type_copy);
+                        break;
+        }
+}
+
+void deferred_smtc_ipi(struct pt_regs *regs)
+{
+        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(regs, pipi);
+                        local_irq_restore(flags);
+                }
+        }
+}
+
+/*
+ * Send clock tick to all TCs except the one executing the funtion
+ */
+
+void smtc_timer_broadcast(int vpe)
+{
+        int cpu;
+        int myTC = cpu_data[smp_processor_id()].tc_id;
+        int myVPE = cpu_data[smp_processor_id()].vpe_id;
+
+        smtc_cpu_stats[smp_processor_id()].timerints++;
+
+        for_each_online_cpu(cpu) {
+                if (cpu_data[cpu].vpe_id == myVPE &&
+                    cpu_data[cpu].tc_id != myTC)
+                        smtc_send_ipi(cpu, SMTC_CLOCK_TICK, 0);
+        }
+}
+
+/*
+ * 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 = MIPSCPU_INT_BASE + MIPS_CPU_IPI_IRQ;
+
+static irqreturn_t ipi_interrupt(int irq, void *dev_idm, struct pt_regs *regs)
+{
+        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;
+        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(regs, pipi);
+                                local_irq_restore(flags);
+                        }
+                }
+        }
+
+        return IRQ_HANDLED;
+}
+
+static void ipi_irq_dispatch(struct pt_regs *regs)
+{
+        do_IRQ(cpu_ipi_irq, regs);
+}
+
+static struct irqaction irq_ipi;
+
+void setup_cross_vpe_interrupts(void)
+{
+        if (!cpu_has_vint)
+                panic("SMTC Kernel requires Vectored Interupt support");
+
+        set_vi_handler(MIPS_CPU_IPI_IRQ, ipi_irq_dispatch);
+
+        irq_ipi.handler = ipi_interrupt;
+        irq_ipi.flags = SA_INTERRUPT;
+        irq_ipi.name = "SMTC_IPI";
+
+        setup_irq_smtc(cpu_ipi_irq, &irq_ipi, (0x100 << MIPS_CPU_IPI_IRQ));
+
+        irq_desc[cpu_ipi_irq].status |= IRQ_PER_CPU;
+}
+
+/*
+ * SMTC-specific hacks invoked from elsewhere in the kernel.
+ */
+
+void smtc_idle_loop_hook(void)
+{
+#ifdef 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 = cpu_data[smp_processor_id()].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()) &&
+                    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, 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 /* SMTC_IDLE_HOOK_DEBUG */
+        /*
+         * 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[smp_processor_id()].depth > 0) {
+                struct smtc_ipi *pipi;
+                extern void self_ipi(struct smtc_ipi *);
+
+                if ((pipi = smtc_ipi_dq(&IPIQ[smp_processor_id()])) != NULL) {
+                        self_ipi(pipi);
+                        smtc_cpu_stats[smp_processor_id()].selfipis++;
+                }
+        }
+}
+
+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, 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 (i = 0; i < num_online_cpus(); 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 (i = 0; i < num_online_cpus(); 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.
+ */
+
+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();
+}