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, 19 insertions, 2 deletions

diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index 2e4cb67f6e56..59af26b54d15 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -39,6 +39,8 @@ enum clock_event_mode {
 	CLOCK_EVT_MODE_PERIODIC,
 	CLOCK_EVT_MODE_ONESHOT,
 	CLOCK_EVT_MODE_RESUME,
+
+	/* Legacy ->set_mode() callback doesn't support below modes */
 };
 
 /*
@@ -81,7 +83,11 @@ enum clock_event_mode {
  * @mode:		operating mode assigned by the management code
  * @features:		features
  * @retries:		number of forced programming retries
- * @set_mode:		set mode function
+ * @set_mode:		legacy set mode function, only for modes <= CLOCK_EVT_MODE_RESUME.
+ * @set_mode_periodic:	switch mode to periodic, if !set_mode
+ * @set_mode_oneshot:	switch mode to oneshot, if !set_mode
+ * @set_mode_shutdown:	switch mode to shutdown, if !set_mode
+ * @set_mode_resume:	resume clkevt device, if !set_mode
  * @broadcast:		function to broadcast events
  * @min_delta_ticks:	minimum delta value in ticks stored for reconfiguration
  * @max_delta_ticks:	maximum delta value in ticks stored for reconfiguration
@@ -108,9 +114,20 @@ struct clock_event_device {
 	unsigned int		features;
 	unsigned long		retries;
 
-	void			(*broadcast)(const struct cpumask *mask);
+	/*
+	 * Mode transition callback(s): Only one of the two groups should be
+	 * defined:
+	 * - set_mode(), only for modes <= CLOCK_EVT_MODE_RESUME.
+	 * - set_mode_{shutdown|periodic|oneshot|resume}().
+	 */
 	void			(*set_mode)(enum clock_event_mode mode,
 					    struct clock_event_device *);
+	int			(*set_mode_periodic)(struct clock_event_device *);
+	int			(*set_mode_oneshot)(struct clock_event_device *);
+	int			(*set_mode_shutdown)(struct clock_event_device *);
+	int			(*set_mode_resume)(struct clock_event_device *);
+
+	void			(*broadcast)(const struct cpumask *mask);
 	void			(*suspend)(struct clock_event_device *);
 	void			(*resume)(struct clock_event_device *);
 	unsigned long		min_delta_ticks;