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>

2 files changed, 79 insertions, 32 deletions

diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 0a1b95f81a32..dadcf824a5cb 100644
--- a/arch/xtensa/Kconfig
+++ b/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
diff --git a/arch/xtensa/kernel/time.c b/arch/xtensa/kernel/time.c
index a32bc2ea7982..ece4f9588625 100644
--- a/arch/xtensa/kernel/time.c
+++ b/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;
 }