[PATCH v3 2/4] cpufreq: introduce cpufreq_driver_might_sleep

[Michael Turquette <mturquette@baylibre.com>]

From: Michael Turquette <mturquette@baylibre.com>

Some architectures and platforms perform CPU frequency transitions
through a non-blocking method, while some might block or sleep. This
distinction is important when trying to change frequency from interrupt
context or in any other non-interruptable context, such as from the
Linux scheduler.

Describe this distinction with a cpufreq driver flag,
CPUFREQ_DRIVER_WILL_NOT_SLEEP. The default is to not have this flag set,
thus erring on the side of caution.

cpufreq_driver_might_sleep() is also introduced in this patch. Setting
the above flag will allow this function to return false.

Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
---
 drivers/cpufreq/cpufreq.c | 6 ++++++
 include/linux/cpufreq.h   | 9 +++++++++
 2 files changed, 15 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 28e59a4..e5296c0 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -112,6 +112,12 @@ bool have_governor_per_policy(void)
 }
 EXPORT_SYMBOL_GPL(have_governor_per_policy);
 
+bool cpufreq_driver_might_sleep(void)
+{
+	return !(cpufreq_driver->flags & CPUFREQ_DRIVER_WILL_NOT_SLEEP);
+}
+EXPORT_SYMBOL_GPL(cpufreq_driver_might_sleep);
+
 struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy)
 {
 	if (have_governor_per_policy())
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 2ee4888..1f2c9a1 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -157,6 +157,7 @@ u64 get_cpu_idle_time(unsigned int cpu, u64 *wall, int io_busy);
 int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu);
 int cpufreq_update_policy(unsigned int cpu);
 bool have_governor_per_policy(void);
+bool cpufreq_driver_might_sleep(void);
 struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy);
 #else
 static inline unsigned int cpufreq_get(unsigned int cpu)
@@ -314,6 +315,14 @@ struct cpufreq_driver {
  */
 #define CPUFREQ_NEED_INITIAL_FREQ_CHECK	(1 << 5)
 
+/*
+ * Set by drivers that will never block or sleep during their frequency
+ * transition. Used to indicate when it is safe to call cpufreq_driver_target
+ * from non-interruptable context. Drivers must opt-in to this flag, as the
+ * safe default is that they might sleep.
+ */
+#define CPUFREQ_DRIVER_WILL_NOT_SLEEP	(1 << 6)
+
 int cpufreq_register_driver(struct cpufreq_driver *driver_data);
 int cpufreq_unregister_driver(struct cpufreq_driver *driver_data);
 
-- 
1.9.1