cpufreq: Support for fast frequency switching
Modify the ACPI cpufreq driver to provide a method for switching
CPU frequencies from interrupt context and update the cpufreq core
to support that method if available.
Introduce a new cpufreq driver callback, ->fast_switch, to be
invoked for frequency switching from interrupt context by (future)
governors supporting that feature via (new) helper function
cpufreq_driver_fast_switch().
Add two new policy flags, fast_switch_possible, to be set by the
cpufreq driver if fast frequency switching can be used for the
given policy and fast_switch_enabled, to be set by the governor
if it is going to use fast frequency switching for the given
policy. Also add a helper for setting the latter.
Since fast frequency switching is inherently incompatible with
cpufreq transition notifiers, make it possible to set the
fast_switch_enabled only if there are no transition notifiers
already registered and make the registration of new transition
notifiers fail if fast_switch_enabled is set for at least one
policy.
Implement the ->fast_switch callback in the ACPI cpufreq driver
and make it set fast_switch_possible during policy initialization
as appropriate.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 2b4f248..55e69eb 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -102,6 +102,17 @@
*/
struct rw_semaphore rwsem;
+ /*
+ * Fast switch flags:
+ * - fast_switch_possible should be set by the driver if it can
+ * guarantee that frequency can be changed on any CPU sharing the
+ * policy and that the change will affect all of the policy CPUs then.
+ * - fast_switch_enabled is to be set by governors that support fast
+ * freqnency switching with the help of cpufreq_enable_fast_switch().
+ */
+ bool fast_switch_possible;
+ bool fast_switch_enabled;
+
/* Synchronization for frequency transitions */
bool transition_ongoing; /* Tracks transition status */
spinlock_t transition_lock;
@@ -156,6 +167,7 @@
int cpufreq_update_policy(unsigned int cpu);
bool have_governor_per_policy(void);
struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy);
+void cpufreq_enable_fast_switch(struct cpufreq_policy *policy);
#else
static inline unsigned int cpufreq_get(unsigned int cpu)
{
@@ -236,6 +248,8 @@
unsigned int relation); /* Deprecated */
int (*target_index)(struct cpufreq_policy *policy,
unsigned int index);
+ unsigned int (*fast_switch)(struct cpufreq_policy *policy,
+ unsigned int target_freq);
/*
* Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION
* unset.
@@ -464,6 +478,8 @@
};
/* Pass a target to the cpufreq driver */
+unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
+ unsigned int target_freq);
int cpufreq_driver_target(struct cpufreq_policy *policy,
unsigned int target_freq,
unsigned int relation);