[MIPS] i8253 PIT clocksource and clockevent drivers

Derived from the i386 variant with a few x86 complexities chopped off.

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

2 files changed, 214 insertions, 0 deletions

diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 7851b4b447d0..a2689f93c160 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -65,6 +65,7 @@ obj-$(CONFIG_PROC_FS)		+= proc.o
 
 obj-$(CONFIG_64BIT)		+= cpu-bugs64.o
 
+obj-$(CONFIG_I8253)		+= i8253.o
 obj-$(CONFIG_PCSPEAKER)		+= pcspeaker.o
 
 obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o
diff --git a/arch/mips/kernel/i8253.c b/arch/mips/kernel/i8253.c
new file mode 100644
index 000000000000..5d9830df3595
--- /dev/null
+++ b/arch/mips/kernel/i8253.c
@@ -0,0 +1,213 @@
+/*
+ * i8253.c  8253/PIT functions
+ *
+ */
+#include <linux/clockchips.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+
+#include <asm/delay.h>
+#include <asm/i8253.h>
+#include <asm/io.h>
+
+static DEFINE_SPINLOCK(i8253_lock);
+
+/*
+ * Initialize the PIT timer.
+ *
+ * This is also called after resume to bring the PIT into operation again.
+ */
+static void init_pit_timer(enum clock_event_mode mode,
+			   struct clock_event_device *evt)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&i8253_lock, flags);
+
+	switch(mode) {
+	case CLOCK_EVT_MODE_PERIODIC:
+		/* binary, mode 2, LSB/MSB, ch 0 */
+		outb_p(0x34, PIT_MODE);
+		outb_p(LATCH & 0xff , PIT_CH0);	/* LSB */
+		outb(LATCH >> 8 , PIT_CH0);	/* MSB */
+		break;
+
+	case CLOCK_EVT_MODE_SHUTDOWN:
+	case CLOCK_EVT_MODE_UNUSED:
+		if (evt->mode == CLOCK_EVT_MODE_PERIODIC ||
+		    evt->mode == CLOCK_EVT_MODE_ONESHOT) {
+			outb_p(0x30, PIT_MODE);
+			outb_p(0, PIT_CH0);
+			outb_p(0, PIT_CH0);
+		}
+		break;
+
+	case CLOCK_EVT_MODE_ONESHOT:
+		/* One shot setup */
+		outb_p(0x38, PIT_MODE);
+		break;
+
+	case CLOCK_EVT_MODE_RESUME:
+		/* Nothing to do here */
+		break;
+	}
+	spin_unlock_irqrestore(&i8253_lock, flags);
+}
+
+/*
+ * Program the next event in oneshot mode
+ *
+ * Delta is given in PIT ticks
+ */
+static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&i8253_lock, flags);
+	outb_p(delta & 0xff , PIT_CH0);	/* LSB */
+	outb(delta >> 8 , PIT_CH0);	/* MSB */
+	spin_unlock_irqrestore(&i8253_lock, flags);
+
+	return 0;
+}
+
+/*
+ * On UP the PIT can serve all of the possible timer functions. On SMP systems
+ * it can be solely used for the global tick.
+ *
+ * The profiling and update capabilites are switched off once the local apic is
+ * registered. This mechanism replaces the previous #ifdef LOCAL_APIC -
+ * !using_apic_timer decisions in do_timer_interrupt_hook()
+ */
+struct clock_event_device pit_clockevent = {
+	.name		= "pit",
+	.features	= CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
+	.set_mode	= init_pit_timer,
+	.set_next_event = pit_next_event,
+	.shift		= 32,
+	.irq		= 0,
+};
+
+irqreturn_t timer_interrupt(int irq, void *dev_id)
+{
+	pit_clockevent.event_handler(&pit_clockevent);
+
+	return IRQ_HANDLED;
+}
+
+static struct irqaction irq0  = {
+	.handler = timer_interrupt,
+	.flags = IRQF_DISABLED | IRQF_NOBALANCING,
+	.mask = CPU_MASK_NONE,
+	.name = "timer"
+};
+
+/*
+ * Initialize the conversion factor and the min/max deltas of the clock event
+ * structure and register the clock event source with the framework.
+ */
+void __init setup_pit_timer(void)
+{
+	/*
+	 * Start pit with the boot cpu mask and make it global after the
+	 * IO_APIC has been initialized.
+	 */
+	pit_clockevent.cpumask = cpumask_of_cpu(0);
+	pit_clockevent.mult = div_sc(CLOCK_TICK_RATE, NSEC_PER_SEC, 32);
+	pit_clockevent.max_delta_ns =
+		clockevent_delta2ns(0x7FFF, &pit_clockevent);
+	pit_clockevent.min_delta_ns =
+		clockevent_delta2ns(0xF, &pit_clockevent);
+	clockevents_register_device(&pit_clockevent);
+
+	irq0.mask = cpumask_of_cpu(0);
+	setup_irq(0, &irq0);
+}
+
+/*
+ * Since the PIT overflows every tick, its not very useful
+ * to just read by itself. So use jiffies to emulate a free
+ * running counter:
+ */
+static cycle_t pit_read(void)
+{
+	unsigned long flags;
+	int count;
+	u32 jifs;
+	static int old_count;
+	static u32 old_jifs;
+
+	spin_lock_irqsave(&i8253_lock, flags);
+	/*
+	 * Although our caller may have the read side of xtime_lock,
+	 * this is now a seqlock, and we are cheating in this routine
+	 * by having side effects on state that we cannot undo if
+	 * there is a collision on the seqlock and our caller has to
+	 * retry.  (Namely, old_jifs and old_count.)  So we must treat
+	 * jiffies as volatile despite the lock.  We read jiffies
+	 * before latching the timer count to guarantee that although
+	 * the jiffies value might be older than the count (that is,
+	 * the counter may underflow between the last point where
+	 * jiffies was incremented and the point where we latch the
+	 * count), it cannot be newer.
+	 */
+	jifs = jiffies;
+	outb_p(0x00, PIT_MODE);	/* latch the count ASAP */
+	count = inb_p(PIT_CH0);	/* read the latched count */
+	count |= inb_p(PIT_CH0) << 8;
+
+	/* VIA686a test code... reset the latch if count > max + 1 */
+	if (count > LATCH) {
+		outb_p(0x34, PIT_MODE);
+		outb_p(LATCH & 0xff, PIT_CH0);
+		outb(LATCH >> 8, PIT_CH0);
+		count = LATCH - 1;
+	}
+
+	/*
+	 * It's possible for count to appear to go the wrong way for a
+	 * couple of reasons:
+	 *
+	 *  1. The timer counter underflows, but we haven't handled the
+	 *     resulting interrupt and incremented jiffies yet.
+	 *  2. Hardware problem with the timer, not giving us continuous time,
+	 *     the counter does small "jumps" upwards on some Pentium systems,
+	 *     (see c't 95/10 page 335 for Neptun bug.)
+	 *
+	 * Previous attempts to handle these cases intelligently were
+	 * buggy, so we just do the simple thing now.
+	 */
+	if (count > old_count && jifs == old_jifs) {
+		count = old_count;
+	}
+	old_count = count;
+	old_jifs = jifs;
+
+	spin_unlock_irqrestore(&i8253_lock, flags);
+
+	count = (LATCH - 1) - count;
+
+	return (cycle_t)(jifs * LATCH) + count;
+}
+
+static struct clocksource clocksource_pit = {
+	.name	= "pit",
+	.rating = 110,
+	.read	= pit_read,
+	.mask	= CLOCKSOURCE_MASK(32),
+	.mult	= 0,
+	.shift	= 20,
+};
+
+static int __init init_pit_clocksource(void)
+{
+	if (num_possible_cpus() > 1) /* PIT does not scale! */
+		return 0;
+
+	clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20);
+	return clocksource_register(&clocksource_pit);
+}
+arch_initcall(init_pit_clocksource);