1 files changed, 159 insertions, 0 deletions

diff --git a/arch/mips/kernel/sync-r4k.c b/arch/mips/kernel/sync-r4k.c
new file mode 100644
index 000000000000..9021108eb9c1
--- /dev/null
+++ b/arch/mips/kernel/sync-r4k.c
@@ -0,0 +1,159 @@
+/*
+ * Count register synchronisation.
+ *
+ * All CPUs will have their count registers synchronised to the CPU0 expirelo
+ * value. This can cause a small timewarp for CPU0. All other CPU's should
+ * not have done anything significant (but they may have had interrupts
+ * enabled briefly - prom_smp_finish() should not be responsible for enabling
+ * interrupts...)
+ *
+ * FIXME: broken for SMTC
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/irqflags.h>
+#include <linux/r4k-timer.h>
+
+#include <asm/atomic.h>
+#include <asm/barrier.h>
+#include <asm/cpumask.h>
+#include <asm/mipsregs.h>
+
+static atomic_t __initdata count_start_flag = ATOMIC_INIT(0);
+static atomic_t __initdata count_count_start = ATOMIC_INIT(0);
+static atomic_t __initdata count_count_stop = ATOMIC_INIT(0);
+
+#define COUNTON 100
+#define NR_LOOPS 5
+
+void __init synchronise_count_master(void)
+{
+        int i;
+        unsigned long flags;
+        unsigned int initcount;
+        int nslaves;
+
+#ifdef CONFIG_MIPS_MT_SMTC
+        /*
+         * SMTC needs to synchronise per VPE, not per CPU
+         * ignore for now
+         */
+        return;
+#endif
+
+        pr_info("Checking COUNT synchronization across %u CPUs: ",
+                num_online_cpus());
+
+        local_irq_save(flags);
+
+        /*
+         * Notify the slaves that it's time to start
+         */
+        atomic_set(&count_start_flag, 1);
+        smp_wmb();
+
+        /* Count will be initialised to expirelo for all CPU's */
+        initcount = expirelo;
+
+        /*
+         * We loop a few times to get a primed instruction cache,
+         * then the last pass is more or less synchronised and
+         * the master and slaves each set their cycle counters to a known
+         * value all at once. This reduces the chance of having random offsets
+         * between the processors, and guarantees that the maximum
+         * delay between the cycle counters is never bigger than
+         * the latency of information-passing (cachelines) between
+         * two CPUs.
+         */
+
+        nslaves = num_online_cpus()-1;
+        for (i = 0; i < NR_LOOPS; i++) {
+                /* slaves loop on '!= ncpus' */
+                while (atomic_read(&count_count_start) != nslaves)
+                        mb();
+                atomic_set(&count_count_stop, 0);
+                smp_wmb();
+
+                /* this lets the slaves write their count register */
+                atomic_inc(&count_count_start);
+
+                /*
+                 * Everyone initialises count in the last loop:
+                 */
+                if (i == NR_LOOPS-1)
+                        write_c0_count(initcount);
+
+                /*
+                 * Wait for all slaves to leave the synchronization point:
+                 */
+                while (atomic_read(&count_count_stop) != nslaves)
+                        mb();
+                atomic_set(&count_count_start, 0);
+                smp_wmb();
+                atomic_inc(&count_count_stop);
+        }
+        /* Arrange for an interrupt in a short while */
+        write_c0_compare(read_c0_count() + COUNTON);
+
+        local_irq_restore(flags);
+
+        /*
+         * i386 code reported the skew here, but the
+         * count registers were almost certainly out of sync
+         * so no point in alarming people
+         */
+        printk("done.\n");
+}
+
+void __init synchronise_count_slave(void)
+{
+        int i;
+        unsigned long flags;
+        unsigned int initcount;
+        int ncpus;
+
+#ifdef CONFIG_MIPS_MT_SMTC
+        /*
+         * SMTC needs to synchronise per VPE, not per CPU
+         * ignore for now
+         */
+        return;
+#endif
+
+        local_irq_save(flags);
+
+        /*
+         * Not every cpu is online at the time this gets called,
+         * so we first wait for the master to say everyone is ready
+         */
+
+        while (!atomic_read(&count_start_flag))
+                mb();
+
+        /* Count will be initialised to expirelo for all CPU's */
+        initcount = expirelo;
+
+        ncpus = num_online_cpus();
+        for (i = 0; i < NR_LOOPS; i++) {
+                atomic_inc(&count_count_start);
+                while (atomic_read(&count_count_start) != ncpus)
+                        mb();
+
+                /*
+                 * Everyone initialises count in the last loop:
+                 */
+                if (i == NR_LOOPS-1)
+                        write_c0_count(initcount);
+
+                atomic_inc(&count_count_stop);
+                while (atomic_read(&count_count_stop) != ncpus)
+                        mb();
+        }
+        /* Arrange for an interrupt in a short while */
+        write_c0_compare(read_c0_count() + COUNTON);
+
+        local_irq_restore(flags);
+}
+#undef NR_LOOPS
+#endif