Fix event timer on Raspberry Pi

- Disable interrupt when updating compare value in order to
   make this operation atomical

- Increase minimum period for event timer. Systimer on BCM2835
    is compare timer, so if minimum period is too small it might
    be less then fraction of time between "read current value" and
    "set compare timer" operations. It means that when timer is armed
    actual counter value is more then compare value and it will take
    whole cycle (~32sec for 1MHz timer) to fire interrupt.

Submitted by:	Daisuke Aoyama <aoyama at peach.ne.jp>

1 files changed, 16 insertions, 2 deletions

diff --git a/sys/arm/broadcom/bcm2835/bcm2835_systimer.c b/sys/arm/broadcom/bcm2835/bcm2835_systimer.c
index 3f5b8da..97ec43a 100644
--- a/sys/arm/broadcom/bcm2835/bcm2835_systimer.c
+++ b/sys/arm/broadcom/bcm2835/bcm2835_systimer.c
@@ -55,6 +55,7 @@ __FBSDID("$FreeBSD$");
 
 #define	DEFAULT_TIMER		3
 #define	DEFAULT_FREQUENCY	1000000
+#define	MIN_PERIOD		100LLU
 
 #define	SYSTIMER_CS	0x00
 #define	SYSTIMER_CLO	0x04
@@ -123,17 +124,24 @@ bcm_systimer_start(struct eventtimer *et, struct bintime *first,
 	struct systimer *st = et->et_priv;
 	uint32_t clo;
 	uint32_t count;
+	register_t s;
 
 	if (first != NULL) {
-		st->enabled = 1;
 
 		count = (st->et.et_frequency * (first->frac >> 32)) >> 32;
 		if (first->sec != 0)
 			count += st->et.et_frequency * first->sec;
 
+		s = intr_disable();
 		clo = bcm_systimer_tc_read_4(SYSTIMER_CLO);
 		clo += count;
+		/*
+		 * Clear pending interrupts
+		 */
+		bcm_systimer_tc_write_4(SYSTIMER_CS, (1 << st->index));
 		bcm_systimer_tc_write_4(SYSTIMER_C0 + st->index*4, clo);
+		st->enabled = 1;
+		intr_restore(s);
 
 		return (0);
 	} 
@@ -154,7 +162,13 @@ static int
 bcm_systimer_intr(void *arg)
 {
 	struct systimer *st = (struct systimer *)arg;
+	uint32_t cs;
+
+ 	cs = bcm_systimer_tc_read_4(SYSTIMER_CS);
+	if ((cs & (1 << st->index)) == 0)
+		return (FILTER_STRAY);
 
+	/* ACK interrupt */
 	bcm_systimer_tc_write_4(SYSTIMER_CS, (1 << st->index));
 	if (st->enabled) {
 		if (st->et.et_active) {
@@ -226,7 +240,7 @@ bcm_systimer_attach(device_t dev)
 	sc->st[DEFAULT_TIMER].et.et_frequency = sc->sysclk_freq;
 	sc->st[DEFAULT_TIMER].et.et_min_period.sec = 0;
 	sc->st[DEFAULT_TIMER].et.et_min_period.frac =
-	    ((0x00000002LLU << 32) / sc->st[DEFAULT_TIMER].et.et_frequency) << 32;
+	    ((MIN_PERIOD << 32) / sc->st[DEFAULT_TIMER].et.et_frequency) << 32;
 	sc->st[DEFAULT_TIMER].et.et_max_period.sec = 0xfffffff0U / sc->st[DEFAULT_TIMER].et.et_frequency;
 	sc->st[DEFAULT_TIMER].et.et_max_period.frac =
 	    ((0xfffffffeLLU << 32) / sc->st[DEFAULT_TIMER].et.et_frequency) << 32;