xtensa: ccount based clockevent implementation

Reused some code from a preliminary implementation by Max Fillippov.

Cc: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Chris Zankel <chris@zankel.net>

arch/xtensa/Kconfig

@@ -6,6 +6,7 @@ config XTENSA
 	select ARCH_WANT_FRAME_POINTERS
 	select HAVE_IDE
 	select GENERIC_ATOMIC64
+	select GENERIC_CLOCKEVENTS
 	select HAVE_GENERIC_HARDIRQS
 	select VIRT_TO_BUS
 	select GENERIC_IRQ_SHOW

arch/xtensa/kernel/time.c

@@ -16,6 +16,7 @@
 #include <linux/sched.h>
 #include <linux/time.h>
 #include <linux/clocksource.h>
+#include <linux/clockchips.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/init.h>
@@ -43,16 +44,80 @@ static struct clocksource ccount_clocksource = {
 	.mask = CLOCKSOURCE_MASK(32),
 };
 
+static int ccount_timer_set_next_event(unsigned long delta,
+		struct clock_event_device *dev);
+static void ccount_timer_set_mode(enum clock_event_mode mode,
+		struct clock_event_device *evt);
+static struct ccount_timer_t {
+	struct clock_event_device evt;
+	int irq_enabled;
+} ccount_timer = {
+	.evt = {
+		.name		= "ccount_clockevent",
+		.features	= CLOCK_EVT_FEAT_ONESHOT,
+		.rating		= 300,
+		.set_next_event	= ccount_timer_set_next_event,
+		.set_mode	= ccount_timer_set_mode,
+	},
+};
+
+static int ccount_timer_set_next_event(unsigned long delta,
+		struct clock_event_device *dev)
+{
+	unsigned long flags, next;
+	int ret = 0;
+
+	local_irq_save(flags);
+	next = get_ccount() + delta;
+	set_linux_timer(next);
+	if (next - get_ccount() > delta)
+		ret = -ETIME;
+	local_irq_restore(flags);
+
+	return ret;
+}
+
+static void ccount_timer_set_mode(enum clock_event_mode mode,
+		struct clock_event_device *evt)
+{
+	struct ccount_timer_t *timer =
+		container_of(evt, struct ccount_timer_t, evt);
+
+	/*
+	 * There is no way to disable the timer interrupt at the device level,
+	 * only at the intenable register itself. Since enable_irq/disable_irq
+	 * calls are nested, we need to make sure that these calls are
+	 * balanced.
+	 */
+	switch (mode) {
+	case CLOCK_EVT_MODE_SHUTDOWN:
+	case CLOCK_EVT_MODE_UNUSED:
+		if (timer->irq_enabled) {
+			disable_irq(evt->irq);
+			timer->irq_enabled = 0;
+		}
+		break;
+	case CLOCK_EVT_MODE_RESUME:
+	case CLOCK_EVT_MODE_ONESHOT:
+		if (!timer->irq_enabled) {
+			enable_irq(evt->irq);
+			timer->irq_enabled = 1;
+		}
+	default:
+		break;
+	}
+}
+
 static irqreturn_t timer_interrupt(int irq, void *dev_id);
 static struct irqaction timer_irqaction = {
 	.handler =	timer_interrupt,
-	.flags =	IRQF_DISABLED,
+	.flags =	IRQF_TIMER,
 	.name =		"timer",
+	.dev_id =	&ccount_timer,
 };
 
 void __init time_init(void)
 {
-	unsigned int irq;
 #ifdef CONFIG_XTENSA_CALIBRATE_CCOUNT
 	printk("Calibrating CPU frequency ");
 	platform_calibrate_ccount();
@@ -61,11 +126,14 @@ void __init time_init(void)
 #endif
 	clocksource_register_hz(&ccount_clocksource, CCOUNT_PER_JIFFY * HZ);
 
-	/* Initialize the linux timer interrupt. */
-
-	irq = irq_create_mapping(NULL, LINUX_TIMER_INT);
-	setup_irq(irq, &timer_irqaction);
-	set_linux_timer(get_ccount() + CCOUNT_PER_JIFFY);
+	ccount_timer.evt.cpumask = cpumask_of(0);
+	ccount_timer.evt.irq = irq_create_mapping(NULL, LINUX_TIMER_INT);
+	if (WARN(!ccount_timer.evt.irq, "error: can't map timer irq"))
+		return;
+	clockevents_config_and_register(&ccount_timer.evt, ccount_freq, 0xf,
+			0xffffffff);
+	setup_irq(ccount_timer.evt.irq, &timer_irqaction);
+	ccount_timer.irq_enabled = 1;
 }
 
 /*
@@ -74,36 +142,14 @@ void __init time_init(void)
 
 irqreturn_t timer_interrupt (int irq, void *dev_id)
 {
+	struct ccount_timer_t *timer = dev_id;
+	struct clock_event_device *evt = &timer->evt;
 
-	unsigned long next;
-
-	next = get_linux_timer();
-
-again:
-	while ((signed long)(get_ccount() - next) > 0) {
-
-		profile_tick(CPU_PROFILING);
-#ifndef CONFIG_SMP
-		update_process_times(user_mode(get_irq_regs()));
-#endif
-
-		xtime_update(1); /* Linux handler in kernel/time/timekeeping */
-
-		/* Note that writing CCOMPARE clears the interrupt. */
-
-		next += CCOUNT_PER_JIFFY;
-		set_linux_timer(next);
-	}
+	evt->event_handler(evt);
 
 	/* Allow platform to do something useful (Wdog). */
-
 	platform_heartbeat();
 
-	/* Make sure we didn't miss any tick... */
-
-	if ((signed long)(get_ccount() - next) > 0)
-		goto again;
-
 	return IRQ_HANDLED;
 }