[MIPS] SMTC: Fix SMTC dyntick support.

Rework of SMTC support to make it work with the new clock event system,
allowing "tickless" operation, and to make it compatible with the use of
the "wait_irqoff" idle loop.  The new clocking scheme means that the
previously optional IPI instant replay mechanism is now required, and has
been made more robust.

Signed-off-by: Kevin D. Kissell <kevink@paralogos.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 133 insertions, 119 deletions

diff --git a/arch/mips/kernel/smtc.c b/arch/mips/kernel/smtc.c
index 39b491b9ad87..897fb2b4751c 100644
--- a/arch/mips/kernel/smtc.c
+++ b/arch/mips/kernel/smtc.c
@@ -1,4 +1,21 @@
-/* Copyright (C) 2004 Mips Technologies, Inc */
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+ *
+ * Copyright (C) 2004 Mips Technologies, Inc
+ * Copyright (C) 2008 Kevin D. Kissell
+ */
 
 #include <linux/clockchips.h>
 #include <linux/kernel.h>
@@ -21,7 +38,6 @@
 #include <asm/time.h>
 #include <asm/addrspace.h>
 #include <asm/smtc.h>
-#include <asm/smtc_ipi.h>
 #include <asm/smtc_proc.h>
 
 /*
@@ -58,11 +74,6 @@ unsigned long irq_hwmask[NR_IRQS];
 
 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
@@ -282,7 +293,7 @@ static void smtc_configure_tlb(void)
  * phys_cpu_present_map and the logical/physical mappings.
  */
 
-int __init mipsmt_build_cpu_map(int start_cpu_slot)
+int __init smtc_build_cpu_map(int start_cpu_slot)
 {
         int i, ntcs;
 
@@ -325,7 +336,12 @@ static void smtc_tc_setup(int vpe, int tc, int cpu)
         write_tc_c0_tcstatus((read_tc_c0_tcstatus()
                         & ~(TCSTATUS_TKSU | TCSTATUS_DA | TCSTATUS_IXMT))
                         | TCSTATUS_A);
-        write_tc_c0_tccontext(0);
+        /*
+         * TCContext gets an offset from the base of the IPIQ array
+         * to be used in low-level code to detect the presence of
+         * an active IPI queue
+         */
+        write_tc_c0_tccontext((sizeof(struct smtc_ipi_q) * cpu) << 16);
         /* Bind tc to vpe */
         write_tc_c0_tcbind(vpe);
         /* In general, all TCs should have the same cpu_data indications */
@@ -336,10 +352,18 @@ static void smtc_tc_setup(int vpe, int tc, int cpu)
                 cpu_data[cpu].options &= ~MIPS_CPU_FPU;
         cpu_data[cpu].vpe_id = vpe;
         cpu_data[cpu].tc_id = tc;
+        /* Multi-core SMTC hasn't been tested, but be prepared */
+        cpu_data[cpu].core = (read_vpe_c0_ebase() >> 1) & 0xff;
 }
 
+/*
+ * Tweak to get Count registes in as close a sync as possible.
+ * Value seems good for 34K-class cores.
+ */
+
+#define CP0_SKEW 8
 
-void mipsmt_prepare_cpus(void)
+void smtc_prepare_cpus(int cpus)
 {
         int i, vpe, tc, ntc, nvpe, tcpervpe[NR_CPUS], slop, cpu;
         unsigned long flags;
@@ -363,13 +387,13 @@ void mipsmt_prepare_cpus(void)
                 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_data[cpu].core = (read_c0_ebase() >> 1) & 0xff;
         cpu++;
 
         /* Report on boot-time options */
@@ -484,7 +508,8 @@ void mipsmt_prepare_cpus(void)
                         write_vpe_c0_compare(0);
                         /* Propagate Config7 */
                         write_vpe_c0_config7(read_c0_config7());
-                        write_vpe_c0_count(read_c0_count());
+                        write_vpe_c0_count(read_c0_count() + CP0_SKEW);
+                        ehb();
                 }
                 /* enable multi-threading within VPE */
                 write_vpe_c0_vpecontrol(read_vpe_c0_vpecontrol() | VPECONTROL_TE);
@@ -585,24 +610,22 @@ void __cpuinit smtc_boot_secondary(int cpu, struct task_struct *idle)
 
 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)
 {
+        int cpu = smp_processor_id();
+
+        /*
+         * Lowest-numbered CPU per VPE starts a clock tick.
+         * Like per_cpu_trap_init() hack, this assumes that
+         * SMTC init code assigns TCs consdecutively and
+         * in ascending order across available VPEs.
+         */
+        if (cpu > 0 && (cpu_data[cpu].vpe_id != cpu_data[cpu - 1].vpe_id))
+                write_c0_compare(read_c0_count() + mips_hpt_frequency/HZ);
+
         printk("TC %d going on-line as CPU %d\n",
                 cpu_data[smp_processor_id()].tc_id, smp_processor_id());
 }
@@ -755,6 +778,8 @@ void smtc_send_ipi(int cpu, int type, unsigned int action)
         struct smtc_ipi *pipi;
         unsigned long flags;
         int mtflags;
+        unsigned long tcrestart;
+        extern void r4k_wait_irqoff(void), __pastwait(void);
 
         if (cpu == smp_processor_id()) {
                 printk("Cannot Send IPI to self!\n");
@@ -771,8 +796,6 @@ void smtc_send_ipi(int cpu, int type, unsigned int action)
         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();
@@ -800,22 +823,29 @@ void smtc_send_ipi(int cpu, int type, unsigned int action)
 
                 if ((tcstatus & TCSTATUS_IXMT) != 0) {
                         /*
-                         * Spin-waiting here can deadlock,
-                         * so we queue the message for the target TC.
+                         * If we're in the the irq-off version of the wait
+                         * loop, we need to force exit from the wait and
+                         * do a direct post of the IPI.
+                         */
+                        if (cpu_wait == r4k_wait_irqoff) {
+                                tcrestart = read_tc_c0_tcrestart();
+                                if (tcrestart >= (unsigned long)r4k_wait_irqoff
+                                    && tcrestart < (unsigned long)__pastwait) {
+                                        write_tc_c0_tcrestart(__pastwait);
+                                        tcstatus &= ~TCSTATUS_IXMT;
+                                        write_tc_c0_tcstatus(tcstatus);
+                                        goto postdirect;
+                                }
+                        }
+                        /*
+                         * Otherwise we queue the message for the target TC
+                         * to pick up when he does a local_irq_restore()
                          */
                         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]);
+postdirect:
                         post_direct_ipi(cpu, pipi);
                         write_tc_c0_tchalt(0);
                         UNLOCK_CORE_PRA();
@@ -883,7 +913,7 @@ static void ipi_call_interrupt(void)
         smp_call_function_interrupt();
 }
 
-DECLARE_PER_CPU(struct clock_event_device, smtc_dummy_clockevent_device);
+DECLARE_PER_CPU(struct clock_event_device, mips_clockevent_device);
 
 void ipi_decode(struct smtc_ipi *pipi)
 {
@@ -891,20 +921,13 @@ void ipi_decode(struct smtc_ipi *pipi)
         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--;
-                }
+                cd = &per_cpu(mips_clockevent_device, cpu);
+                cd->event_handler(cd);
                 irq_exit();
                 break;
 
@@ -937,24 +960,48 @@ void ipi_decode(struct smtc_ipi *pipi)
         }
 }
 
+/*
+ * Similar to smtc_ipi_replay(), but invoked from context restore,
+ * so it reuses the current exception frame rather than set up a
+ * new one with self_ipi.
+ */
+
 void deferred_smtc_ipi(void)
 {
-        struct smtc_ipi *pipi;
-        unsigned long flags;
-/* DEBUG */
-        int q = smp_processor_id();
+        int cpu = 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 irq_disabled when this was called, then any IPIs queued
+         * after we test last will be taken on the next irq_enable/restore.
+         * If interrupts were enabled, then any IPIs added after the
+         * last test will be taken directly.
          */
-        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);
+
+        while (IPIQ[cpu].head != NULL) {
+                struct smtc_ipi_q *q = &IPIQ[cpu];
+                struct smtc_ipi *pipi;
+                unsigned long flags;
+
+                /*
+                 * It may be possible we'll come in with interrupts
+                 * already enabled.
+                 */
+                local_irq_save(flags);
+
+                spin_lock(&q->lock);
+                pipi = __smtc_ipi_dq(q);
+                spin_unlock(&q->lock);
+                if (pipi != NULL)
                         ipi_decode(pipi);
-                        local_irq_restore(flags);
-                }
+                /*
+                 * The use of the __raw_local restore isn't
+                 * as obviously necessary here as in smtc_ipi_replay(),
+                 * but it's more efficient, given that we're already
+                 * running down the IPI queue.
+                 */
+                __raw_local_irq_restore(flags);
         }
 }
 
@@ -1066,55 +1113,53 @@ static void setup_cross_vpe_interrupts(unsigned int nvpe)
 
 /*
  * 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)
+ /*
+  * smtc_ipi_replay is called from raw_local_irq_restore
+  */
+
+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.
+         * and not a pseudo-pseudo interrupt.  The important thing
+         * is to do the last check for queued message *after* the
+         * re-enabling of interrupts.
          */
-        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;
+        while (IPIQ[cpu].head != NULL) {
+                struct smtc_ipi_q *q = &IPIQ[cpu];
+                struct smtc_ipi *pipi;
+                unsigned long flags;
 
+                /*
+                 * It's just possible we'll come in with interrupts
+                 * already enabled.
+                 */
+                local_irq_save(flags);
+
+                spin_lock(&q->lock);
+                pipi = __smtc_ipi_dq(q);
+                spin_unlock(&q->lock);
+                /*
+                 ** But use a raw restore here to avoid recursion.
+                 */
+                __raw_local_irq_restore(flags);
+
+                if (pipi) {
                         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)
@@ -1193,40 +1238,13 @@ void smtc_idle_loop_hook(void)
                 }
         }
 
-        /*
-         * 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 */
+        smtc_ipi_replay();
 }
 
 void smtc_soft_dump(void)
@@ -1242,10 +1260,6 @@ void smtc_soft_dump(void)
                 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));
 }