clockevents: Introduce mode specific callbacks

It is not possible for the clockevents core to know which modes (other than
those with a corresponding feature flag) are supported by a particular
implementation. And drivers are expected to handle transition to all modes
elegantly, as ->set_mode() would be issued for them unconditionally.

Now, adding support for a new mode complicates things a bit if we want to use
the legacy ->set_mode() callback. We need to closely review all clockevents
drivers to see if they would break on addition of a new mode. And after such
reviews, it is found that we have to do non-trivial changes to most of the
drivers [1].

Introduce mode-specific set_mode_*() callbacks, some of which the drivers may or
may not implement. A missing callback would clearly convey the message that the
corresponding mode isn't supported.

A driver may still choose to keep supporting the legacy ->set_mode() callback,
but ->set_mode() wouldn't be supporting any new modes beyond RESUME. If a driver
wants to benefit from using a new mode, it would be required to migrate to
the mode specific callbacks.

The legacy ->set_mode() callback and the newly introduced mode-specific
callbacks are mutually exclusive. Only one of them should be supported by the
driver.

Sanity check is done at the time of registration to distinguish between optional
and required callbacks and to make error recovery and handling simpler. If the
legacy ->set_mode() callback is provided, all mode specific ones would be
ignored by the core but a warning is thrown if they are present.

Call sites calling ->set_mode() directly are also updated to use
__clockevents_set_mode() instead, as ->set_mode() may not be available anymore
for few drivers.

 [1] https://lkml.org/lkml/2014/12/9/605
 [2] https://lkml.org/lkml/2015/1/23/255

Suggested-by: Thomas Gleixner <tglx@linutronix.de> [2]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: linaro-kernel@lists.linaro.org
Cc: linaro-networking@linaro.org
Link: http://lkml.kernel.org/r/792d59a40423f0acffc9bb0bec9de1341a06fa02.1423788565.git.viresh.kumar@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 86 insertions, 2 deletions

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 55449909f114..489642b08d64 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -94,6 +94,57 @@ u64 clockevent_delta2ns(unsigned long latch, struct clock_event_device *evt)
 }
 EXPORT_SYMBOL_GPL(clockevent_delta2ns);
 
+static int __clockevents_set_mode(struct clock_event_device *dev,
+                                  enum clock_event_mode mode)
+{
+        /* Transition with legacy set_mode() callback */
+        if (dev->set_mode) {
+                /* Legacy callback doesn't support new modes */
+                if (mode > CLOCK_EVT_MODE_RESUME)
+                        return -ENOSYS;
+                dev->set_mode(mode, dev);
+                return 0;
+        }
+
+        if (dev->features & CLOCK_EVT_FEAT_DUMMY)
+                return 0;
+
+        /* Transition with new mode-specific callbacks */
+        switch (mode) {
+        case CLOCK_EVT_MODE_UNUSED:
+                /*
+                 * This is an internal state, which is guaranteed to go from
+                 * SHUTDOWN to UNUSED. No driver interaction required.
+                 */
+                return 0;
+
+        case CLOCK_EVT_MODE_SHUTDOWN:
+                return dev->set_mode_shutdown(dev);
+
+        case CLOCK_EVT_MODE_PERIODIC:
+                /* Core internal bug */
+                if (!(dev->features & CLOCK_EVT_FEAT_PERIODIC))
+                        return -ENOSYS;
+                return dev->set_mode_periodic(dev);
+
+        case CLOCK_EVT_MODE_ONESHOT:
+                /* Core internal bug */
+                if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT))
+                        return -ENOSYS;
+                return dev->set_mode_oneshot(dev);
+
+        case CLOCK_EVT_MODE_RESUME:
+                /* Optional callback */
+                if (dev->set_mode_resume)
+                        return dev->set_mode_resume(dev);
+                else
+                        return 0;
+
+        default:
+                return -ENOSYS;
+        }
+}
+
 /**
  * clockevents_set_mode - set the operating mode of a clock event device
  * @dev:        device to modify
@@ -105,7 +156,9 @@ void clockevents_set_mode(struct clock_event_device *dev,
                                  enum clock_event_mode mode)
 {
         if (dev->mode != mode) {
-                dev->set_mode(mode, dev);
+                if (__clockevents_set_mode(dev, mode))
+                        return;
+
                 dev->mode = mode;
 
                 /*
@@ -373,6 +426,35 @@ int clockevents_unbind_device(struct clock_event_device *ced, int cpu)
 }
 EXPORT_SYMBOL_GPL(clockevents_unbind);
 
+/* Sanity check of mode transition callbacks */
+static int clockevents_sanity_check(struct clock_event_device *dev)
+{
+        /* Legacy set_mode() callback */
+        if (dev->set_mode) {
+                /* We shouldn't be supporting new modes now */
+                WARN_ON(dev->set_mode_periodic || dev->set_mode_oneshot ||
+                        dev->set_mode_shutdown || dev->set_mode_resume);
+                return 0;
+        }
+
+        if (dev->features & CLOCK_EVT_FEAT_DUMMY)
+                return 0;
+
+        /* New mode-specific callbacks */
+        if (!dev->set_mode_shutdown)
+                return -EINVAL;
+
+        if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&
+            !dev->set_mode_periodic)
+                return -EINVAL;
+
+        if ((dev->features & CLOCK_EVT_FEAT_ONESHOT) &&
+            !dev->set_mode_oneshot)
+                return -EINVAL;
+
+        return 0;
+}
+
 /**
  * clockevents_register_device - register a clock event device
  * @dev:        device to register
@@ -382,6 +464,8 @@ void clockevents_register_device(struct clock_event_device *dev)
         unsigned long flags;
 
         BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
+        BUG_ON(clockevents_sanity_check(dev));
+
         if (!dev->cpumask) {
                 WARN_ON(num_possible_cpus() > 1);
                 dev->cpumask = cpumask_of(smp_processor_id());
@@ -449,7 +533,7 @@ int __clockevents_update_freq(struct clock_event_device *dev, u32 freq)
                 return clockevents_program_event(dev, dev->next_event, false);
 
         if (dev->mode == CLOCK_EVT_MODE_PERIODIC)
-                dev->set_mode(CLOCK_EVT_MODE_PERIODIC, dev);
+                return __clockevents_set_mode(dev, CLOCK_EVT_MODE_PERIODIC);
 
         return 0;
 }