clockevents: Introduce CLOCK_EVT_STATE_ONESHOT_STOPPED state

When no timers/hrtimers are pending, the expiry time is set to a
special value: 'KTIME_MAX'. This normally happens with
NO_HZ_{IDLE|FULL} in both LOWRES/HIGHRES modes.

When 'expiry == KTIME_MAX', we either cancel the 'tick-sched' hrtimer
(NOHZ_MODE_HIGHRES) or skip reprogramming clockevent device
(NOHZ_MODE_LOWRES).  But, the clockevent device is already
reprogrammed from the tick-handler for next tick.

As the clock event device is programmed in ONESHOT mode it will at
least fire one more time (unnecessarily). Timers on few
implementations (like arm_arch_timer, etc.) only support PERIODIC mode
and their drivers emulate ONESHOT over that. Which means that on these
platforms we will get spurious interrupts periodically (at last
programmed interval rate, normally tick rate).

In order to avoid spurious interrupts, the clockevent device should be
stopped or its interrupts should be masked.

A simple (yet hacky) solution to get this fixed could be: update
hrtimer_force_reprogram() to always reprogram clockevent device and
update clockevent drivers to STOP generating events (or delay it to
max time) when 'expires' is set to KTIME_MAX. But the drawback here is
that every clockevent driver has to be hacked for this particular case
and its very easy for new ones to miss this.

However, Thomas suggested to add an optional state ONESHOT_STOPPED to
solve this problem: lkml.org/lkml/2014/5/9/508.

This patch adds support for ONESHOT_STOPPED state in clockevents
core. It will only be available to drivers that implement the
state-specific callbacks instead of the legacy ->set_mode() callback.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Preeti U. Murthy <preeti@linux.vnet.ibm.com>
Cc: linaro-kernel@lists.linaro.org
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/b8b383a03ac07b13312c16850b5106b82e4245b5.1428031396.git.viresh.kumar@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index 96c280b2c263476c053bdd0c514aa16df3d04212..271fa4c8eb29fea43a2b8412c30f8f982cf2cc2e 100644 (file)
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -37,12 +37,15 @@ enum clock_event_mode {
  *             reached from DETACHED or SHUTDOWN.
  * ONESHOT:    Device is programmed to generate event only once. Can be reached
  *             from DETACHED or SHUTDOWN.
+ * ONESHOT_STOPPED: Device was programmed in ONESHOT mode and is temporarily
+ *                 stopped.
  */
 enum clock_event_state {
        CLOCK_EVT_STATE_DETACHED,
        CLOCK_EVT_STATE_SHUTDOWN,
        CLOCK_EVT_STATE_PERIODIC,
        CLOCK_EVT_STATE_ONESHOT,
+       CLOCK_EVT_STATE_ONESHOT_STOPPED,
 };
 
 /*
@@ -90,6 +93,7 @@ enum clock_event_state {
  * @set_mode:          legacy set mode function, only for modes <= CLOCK_EVT_MODE_RESUME.
  * @set_state_periodic:        switch state to periodic, if !set_mode
  * @set_state_oneshot: switch state to oneshot, if !set_mode
+ * @set_state_oneshot_stopped: switch state to oneshot_stopped, if !set_mode
  * @set_state_shutdown:        switch state to shutdown, if !set_mode
  * @tick_resume:       resume clkevt device, if !set_mode
  * @broadcast:         function to broadcast events
@@ -121,11 +125,12 @@ struct clock_event_device {
         * State transition callback(s): Only one of the two groups should be
         * defined:
         * - set_mode(), only for modes <= CLOCK_EVT_MODE_RESUME.
-        * - set_state_{shutdown|periodic|oneshot}(), tick_resume().
+        * - set_state_{shutdown|periodic|oneshot|oneshot_stopped}(), tick_resume().
         */
        void                    (*set_mode)(enum clock_event_mode mode, struct clock_event_device *);
        int                     (*set_state_periodic)(struct clock_event_device *);
        int                     (*set_state_oneshot)(struct clock_event_device *);
+       int                     (*set_state_oneshot_stopped)(struct clock_event_device *);
        int                     (*set_state_shutdown)(struct clock_event_device *);
        int                     (*tick_resume)(struct clock_event_device *);
 

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 637a09461c1d9a3d30fc3d6a33cb85b76a990261..dc6afb4850272c8515b70caae5aef4967b28fcd7 100644 (file)
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -134,6 +134,17 @@ static int __clockevents_set_state(struct clock_event_device *dev,
                        return -ENOSYS;
                return dev->set_state_oneshot(dev);
 
+       case CLOCK_EVT_STATE_ONESHOT_STOPPED:
+               /* Core internal bug */
+               if (WARN_ONCE(dev->state != CLOCK_EVT_STATE_ONESHOT,
+                             "Current state: %d\n", dev->state))
+                       return -EINVAL;
+
+               if (dev->set_state_oneshot_stopped)
+                       return dev->set_state_oneshot_stopped(dev);
+               else
+                       return -ENOSYS;
+
        default:
                return -ENOSYS;
        }
@@ -445,7 +456,8 @@ static int clockevents_sanity_check(struct clock_event_device *dev)
        if (dev->set_mode) {
                /* We shouldn't be supporting new modes now */
                WARN_ON(dev->set_state_periodic || dev->set_state_oneshot ||
-                       dev->set_state_shutdown || dev->tick_resume);
+                       dev->set_state_shutdown || dev->tick_resume ||
+                       dev->set_state_oneshot_stopped);
 
                BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
                return 0;

diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
index 18b074b215b0a171b9411cd1c8154c3a47b59ce8..1327004429be6fee0b29a7aa9a19ff16a31362e2 100644 (file)
--- a/kernel/time/timer_list.c
+++ b/kernel/time/timer_list.c
@@ -258,6 +258,12 @@ print_tickdevice(struct seq_file *m, struct tick_device *td, int cpu)
                        SEQ_printf(m, "\n");
                }
 
+               if (dev->set_state_oneshot_stopped) {
+                       SEQ_printf(m, " oneshot stopped: ");
+                       print_name_offset(m, dev->set_state_oneshot_stopped);
+                       SEQ_printf(m, "\n");
+               }
+
                if (dev->tick_resume) {
                        SEQ_printf(m, " resume:   ");
                        print_name_offset(m, dev->tick_resume);