1 files changed, 298 insertions, 0 deletions
diff --git a/arch/mips/kernel/cevt-r4k.c b/arch/mips/kernel/cevt-r4k.c
new file mode 100644
index 000000000..dd6a18bc1
--- /dev/null
+++ b/arch/mips/kernel/cevt-r4k.c
@@ -0,0 +1,298 @@
+/*
+ * 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/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;
+
+#ifdef CONFIG_KVM_GUEST
+    return 1;
+#endif
+
+	/*
+	 * 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;
+}
+
+int r4k_clockevent_init(void)
+{
+	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;
+
+	setup_irq(irq, &c0_compare_irqaction);
+
+	return 0;
+}
+