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-rw-r--r--arch/mips/kernel/cevt-r4k.c341
1 files changed, 341 insertions, 0 deletions
diff --git a/arch/mips/kernel/cevt-r4k.c b/arch/mips/kernel/cevt-r4k.c
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+++ b/arch/mips/kernel/cevt-r4k.c
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+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2007 MIPS Technologies, Inc.
+ * Copyright (C) 2007 Ralf Baechle <ralf@linux-mips.org>
+ */
+#include <linux/clockchips.h>
+#include <linux/interrupt.h>
+#include <linux/cpufreq.h>
+#include <linux/percpu.h>
+#include <linux/smp.h>
+#include <linux/irq.h>
+
+#include <asm/time.h>
+#include <asm/cevt-r4k.h>
+
+static int mips_next_event(unsigned long delta,
+ struct clock_event_device *evt)
+{
+ unsigned int cnt;
+ int res;
+
+ cnt = read_c0_count();
+ cnt += delta;
+ write_c0_compare(cnt);
+ res = ((int)(read_c0_count() - cnt) >= 0) ? -ETIME : 0;
+ return res;
+}
+
+/**
+ * calculate_min_delta() - Calculate a good minimum delta for mips_next_event().
+ *
+ * Running under virtualisation can introduce overhead into mips_next_event() in
+ * the form of hypervisor emulation of CP0_Count/CP0_Compare registers,
+ * potentially with an unnatural frequency, which makes a fixed min_delta_ns
+ * value inappropriate as it may be too small.
+ *
+ * It can also introduce occasional latency from the guest being descheduled.
+ *
+ * This function calculates a good minimum delta based roughly on the 75th
+ * percentile of the time taken to do the mips_next_event() sequence, in order
+ * to handle potentially higher overhead while also eliminating outliers due to
+ * unpredictable hypervisor latency (which can be handled by retries).
+ *
+ * Return: An appropriate minimum delta for the clock event device.
+ */
+static unsigned int calculate_min_delta(void)
+{
+ unsigned int cnt, i, j, k, l;
+ unsigned int buf1[4], buf2[3];
+ unsigned int min_delta;
+
+ /*
+ * Calculate the median of 5 75th percentiles of 5 samples of how long
+ * it takes to set CP0_Compare = CP0_Count + delta.
+ */
+ for (i = 0; i < 5; ++i) {
+ for (j = 0; j < 5; ++j) {
+ /*
+ * This is like the code in mips_next_event(), and
+ * directly measures the borderline "safe" delta.
+ */
+ cnt = read_c0_count();
+ write_c0_compare(cnt);
+ cnt = read_c0_count() - cnt;
+
+ /* Sorted insert into buf1 */
+ for (k = 0; k < j; ++k) {
+ if (cnt < buf1[k]) {
+ l = min_t(unsigned int,
+ j, ARRAY_SIZE(buf1) - 1);
+ for (; l > k; --l)
+ buf1[l] = buf1[l - 1];
+ break;
+ }
+ }
+ if (k < ARRAY_SIZE(buf1))
+ buf1[k] = cnt;
+ }
+
+ /* Sorted insert of 75th percentile into buf2 */
+ for (k = 0; k < i && k < ARRAY_SIZE(buf2); ++k) {
+ if (buf1[ARRAY_SIZE(buf1) - 1] < buf2[k]) {
+ l = min_t(unsigned int,
+ i, ARRAY_SIZE(buf2) - 1);
+ for (; l > k; --l)
+ buf2[l] = buf2[l - 1];
+ break;
+ }
+ }
+ if (k < ARRAY_SIZE(buf2))
+ buf2[k] = buf1[ARRAY_SIZE(buf1) - 1];
+ }
+
+ /* Use 2 * median of 75th percentiles */
+ min_delta = buf2[ARRAY_SIZE(buf2) - 1] * 2;
+
+ /* Don't go too low */
+ if (min_delta < 0x300)
+ min_delta = 0x300;
+
+ pr_debug("%s: median 75th percentile=%#x, min_delta=%#x\n",
+ __func__, buf2[ARRAY_SIZE(buf2) - 1], min_delta);
+ return min_delta;
+}
+
+DEFINE_PER_CPU(struct clock_event_device, mips_clockevent_device);
+int cp0_timer_irq_installed;
+
+/*
+ * Possibly handle a performance counter interrupt.
+ * Return true if the timer interrupt should not be checked
+ */
+static inline int handle_perf_irq(int r2)
+{
+ /*
+ * The performance counter overflow interrupt may be shared with the
+ * timer interrupt (cp0_perfcount_irq < 0). If it is and a
+ * performance counter has overflowed (perf_irq() == IRQ_HANDLED)
+ * and we can't reliably determine if a counter interrupt has also
+ * happened (!r2) then don't check for a timer interrupt.
+ */
+ return (cp0_perfcount_irq < 0) &&
+ perf_irq() == IRQ_HANDLED &&
+ !r2;
+}
+
+irqreturn_t c0_compare_interrupt(int irq, void *dev_id)
+{
+ const int r2 = cpu_has_mips_r2_r6;
+ struct clock_event_device *cd;
+ int cpu = smp_processor_id();
+
+ /*
+ * Suckage alert:
+ * Before R2 of the architecture there was no way to see if a
+ * performance counter interrupt was pending, so we have to run
+ * the performance counter interrupt handler anyway.
+ */
+ if (handle_perf_irq(r2))
+ return IRQ_HANDLED;
+
+ /*
+ * The same applies to performance counter interrupts. But with the
+ * above we now know that the reason we got here must be a timer
+ * interrupt. Being the paranoiacs we are we check anyway.
+ */
+ if (!r2 || (read_c0_cause() & CAUSEF_TI)) {
+ /* Clear Count/Compare Interrupt */
+ write_c0_compare(read_c0_compare());
+ cd = &per_cpu(mips_clockevent_device, cpu);
+ cd->event_handler(cd);
+
+ return IRQ_HANDLED;
+ }
+
+ return IRQ_NONE;
+}
+
+struct irqaction c0_compare_irqaction = {
+ .handler = c0_compare_interrupt,
+ /*
+ * IRQF_SHARED: The timer interrupt may be shared with other interrupts
+ * such as perf counter and FDC interrupts.
+ */
+ .flags = IRQF_PERCPU | IRQF_TIMER | IRQF_SHARED,
+ .name = "timer",
+};
+
+
+void mips_event_handler(struct clock_event_device *dev)
+{
+}
+
+/*
+ * FIXME: This doesn't hold for the relocated E9000 compare interrupt.
+ */
+static int c0_compare_int_pending(void)
+{
+ /* When cpu_has_mips_r2, this checks Cause.TI instead of Cause.IP7 */
+ return (read_c0_cause() >> cp0_compare_irq_shift) & (1ul << CAUSEB_IP);
+}
+
+/*
+ * Compare interrupt can be routed and latched outside the core,
+ * so wait up to worst case number of cycle counter ticks for timer interrupt
+ * changes to propagate to the cause register.
+ */
+#define COMPARE_INT_SEEN_TICKS 50
+
+int c0_compare_int_usable(void)
+{
+ unsigned int delta;
+ unsigned int cnt;
+
+ /*
+ * IP7 already pending? Try to clear it by acking the timer.
+ */
+ if (c0_compare_int_pending()) {
+ cnt = read_c0_count();
+ write_c0_compare(cnt);
+ back_to_back_c0_hazard();
+ while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
+ if (!c0_compare_int_pending())
+ break;
+ if (c0_compare_int_pending())
+ return 0;
+ }
+
+ for (delta = 0x10; delta <= 0x400000; delta <<= 1) {
+ cnt = read_c0_count();
+ cnt += delta;
+ write_c0_compare(cnt);
+ back_to_back_c0_hazard();
+ if ((int)(read_c0_count() - cnt) < 0)
+ break;
+ /* increase delta if the timer was already expired */
+ }
+
+ while ((int)(read_c0_count() - cnt) <= 0)
+ ; /* Wait for expiry */
+
+ while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
+ if (c0_compare_int_pending())
+ break;
+ if (!c0_compare_int_pending())
+ return 0;
+ cnt = read_c0_count();
+ write_c0_compare(cnt);
+ back_to_back_c0_hazard();
+ while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
+ if (!c0_compare_int_pending())
+ break;
+ if (c0_compare_int_pending())
+ return 0;
+
+ /*
+ * Feels like a real count / compare timer.
+ */
+ return 1;
+}
+
+unsigned int __weak get_c0_compare_int(void)
+{
+ return MIPS_CPU_IRQ_BASE + cp0_compare_irq;
+}
+
+#ifdef CONFIG_CPU_FREQ
+
+static unsigned long mips_ref_freq;
+
+static int r4k_cpufreq_callback(struct notifier_block *nb,
+ unsigned long val, void *data)
+{
+ struct cpufreq_freqs *freq = data;
+ struct clock_event_device *cd;
+ unsigned long rate;
+ int cpu;
+
+ if (!mips_ref_freq)
+ mips_ref_freq = freq->old;
+
+ if (val == CPUFREQ_POSTCHANGE) {
+ rate = cpufreq_scale(mips_hpt_frequency, mips_ref_freq,
+ freq->new);
+
+ for_each_cpu(cpu, freq->policy->cpus) {
+ cd = &per_cpu(mips_clockevent_device, cpu);
+
+ clockevents_update_freq(cd, rate);
+ }
+ }
+
+ return 0;
+}
+
+static struct notifier_block r4k_cpufreq_notifier = {
+ .notifier_call = r4k_cpufreq_callback,
+};
+
+static int __init r4k_register_cpufreq_notifier(void)
+{
+ return cpufreq_register_notifier(&r4k_cpufreq_notifier,
+ CPUFREQ_TRANSITION_NOTIFIER);
+
+}
+core_initcall(r4k_register_cpufreq_notifier);
+
+#endif /* !CONFIG_CPU_FREQ */
+
+int r4k_clockevent_init(void)
+{
+ unsigned long flags = IRQF_PERCPU | IRQF_TIMER | IRQF_SHARED;
+ unsigned int cpu = smp_processor_id();
+ struct clock_event_device *cd;
+ unsigned int irq, min_delta;
+
+ if (!cpu_has_counter || !mips_hpt_frequency)
+ return -ENXIO;
+
+ if (!c0_compare_int_usable())
+ return -ENXIO;
+
+ /*
+ * With vectored interrupts things are getting platform specific.
+ * get_c0_compare_int is a hook to allow a platform to return the
+ * interrupt number of its liking.
+ */
+ irq = get_c0_compare_int();
+
+ cd = &per_cpu(mips_clockevent_device, cpu);
+
+ cd->name = "MIPS";
+ cd->features = CLOCK_EVT_FEAT_ONESHOT |
+ CLOCK_EVT_FEAT_C3STOP |
+ CLOCK_EVT_FEAT_PERCPU;
+
+ min_delta = calculate_min_delta();
+
+ cd->rating = 300;
+ cd->irq = irq;
+ cd->cpumask = cpumask_of(cpu);
+ cd->set_next_event = mips_next_event;
+ cd->event_handler = mips_event_handler;
+
+ clockevents_config_and_register(cd, mips_hpt_frequency, min_delta, 0x7fffffff);
+
+ if (cp0_timer_irq_installed)
+ return 0;
+
+ cp0_timer_irq_installed = 1;
+
+ if (request_irq(irq, c0_compare_interrupt, flags, "timer",
+ c0_compare_interrupt))
+ pr_err("Failed to request irq %d (timer)\n", irq);
+
+ return 0;
+}
+