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/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index b87596b..a5b7d77 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -77,6 +77,7 @@
static int cpufreq_governor(struct cpufreq_policy *policy, unsigned int event);
static unsigned int __cpufreq_get(struct cpufreq_policy *policy);
static int cpufreq_start_governor(struct cpufreq_policy *policy);
+static int cpufreq_exit_governor(struct cpufreq_policy *policy);
/**
* Two notifier lists: the "policy" list is involved in the
@@ -429,6 +430,68 @@
}
EXPORT_SYMBOL_GPL(cpufreq_freq_transition_end);
+/*
+ * Fast frequency switching status count. Positive means "enabled", negative
+ * means "disabled" and 0 means "not decided yet".
+ */
+static int cpufreq_fast_switch_count;
+static DEFINE_MUTEX(cpufreq_fast_switch_lock);
+
+static void cpufreq_list_transition_notifiers(void)
+{
+ struct notifier_block *nb;
+
+ pr_info("Registered transition notifiers:\n");
+
+ mutex_lock(&cpufreq_transition_notifier_list.mutex);
+
+ for (nb = cpufreq_transition_notifier_list.head; nb; nb = nb->next)
+ pr_info("%pF\n", nb->notifier_call);
+
+ mutex_unlock(&cpufreq_transition_notifier_list.mutex);
+}
+
+/**
+ * cpufreq_enable_fast_switch - Enable fast frequency switching for policy.
+ * @policy: cpufreq policy to enable fast frequency switching for.
+ *
+ * Try to enable fast frequency switching for @policy.
+ *
+ * The attempt will fail if there is at least one transition notifier registered
+ * at this point, as fast frequency switching is quite fundamentally at odds
+ * with transition notifiers. Thus if successful, it will make registration of
+ * transition notifiers fail going forward.
+ */
+void cpufreq_enable_fast_switch(struct cpufreq_policy *policy)
+{
+ lockdep_assert_held(&policy->rwsem);
+
+ if (!policy->fast_switch_possible)
+ return;
+
+ mutex_lock(&cpufreq_fast_switch_lock);
+ if (cpufreq_fast_switch_count >= 0) {
+ cpufreq_fast_switch_count++;
+ policy->fast_switch_enabled = true;
+ } else {
+ pr_warn("CPU%u: Fast frequency switching not enabled\n",
+ policy->cpu);
+ cpufreq_list_transition_notifiers();
+ }
+ mutex_unlock(&cpufreq_fast_switch_lock);
+}
+EXPORT_SYMBOL_GPL(cpufreq_enable_fast_switch);
+
+static void cpufreq_disable_fast_switch(struct cpufreq_policy *policy)
+{
+ mutex_lock(&cpufreq_fast_switch_lock);
+ if (policy->fast_switch_enabled) {
+ policy->fast_switch_enabled = false;
+ if (!WARN_ON(cpufreq_fast_switch_count <= 0))
+ cpufreq_fast_switch_count--;
+ }
+ mutex_unlock(&cpufreq_fast_switch_lock);
+}
/*********************************************************************
* SYSFS INTERFACE *
@@ -1319,7 +1382,7 @@
/* If cpu is last user of policy, free policy */
if (has_target()) {
- ret = cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
+ ret = cpufreq_exit_governor(policy);
if (ret)
pr_err("%s: Failed to exit governor\n", __func__);
}
@@ -1447,8 +1510,12 @@
ret_freq = cpufreq_driver->get(policy->cpu);
- /* Updating inactive policies is invalid, so avoid doing that. */
- if (unlikely(policy_is_inactive(policy)))
+ /*
+ * Updating inactive policies is invalid, so avoid doing that. Also
+ * if fast frequency switching is used with the given policy, the check
+ * against policy->cur is pointless, so skip it in that case too.
+ */
+ if (unlikely(policy_is_inactive(policy)) || policy->fast_switch_enabled)
return ret_freq;
if (ret_freq && policy->cur &&
@@ -1672,8 +1739,18 @@
switch (list) {
case CPUFREQ_TRANSITION_NOTIFIER:
+ mutex_lock(&cpufreq_fast_switch_lock);
+
+ if (cpufreq_fast_switch_count > 0) {
+ mutex_unlock(&cpufreq_fast_switch_lock);
+ return -EBUSY;
+ }
ret = srcu_notifier_chain_register(
&cpufreq_transition_notifier_list, nb);
+ if (!ret)
+ cpufreq_fast_switch_count--;
+
+ mutex_unlock(&cpufreq_fast_switch_lock);
break;
case CPUFREQ_POLICY_NOTIFIER:
ret = blocking_notifier_chain_register(
@@ -1706,8 +1783,14 @@
switch (list) {
case CPUFREQ_TRANSITION_NOTIFIER:
+ mutex_lock(&cpufreq_fast_switch_lock);
+
ret = srcu_notifier_chain_unregister(
&cpufreq_transition_notifier_list, nb);
+ if (!ret && !WARN_ON(cpufreq_fast_switch_count >= 0))
+ cpufreq_fast_switch_count++;
+
+ mutex_unlock(&cpufreq_fast_switch_lock);
break;
case CPUFREQ_POLICY_NOTIFIER:
ret = blocking_notifier_chain_unregister(
@@ -1726,6 +1809,37 @@
* GOVERNORS *
*********************************************************************/
+/**
+ * cpufreq_driver_fast_switch - Carry out a fast CPU frequency switch.
+ * @policy: cpufreq policy to switch the frequency for.
+ * @target_freq: New frequency to set (may be approximate).
+ *
+ * Carry out a fast frequency switch without sleeping.
+ *
+ * The driver's ->fast_switch() callback invoked by this function must be
+ * suitable for being called from within RCU-sched read-side critical sections
+ * and it is expected to select the minimum available frequency greater than or
+ * equal to @target_freq (CPUFREQ_RELATION_L).
+ *
+ * This function must not be called if policy->fast_switch_enabled is unset.
+ *
+ * Governors calling this function must guarantee that it will never be invoked
+ * twice in parallel for the same policy and that it will never be called in
+ * parallel with either ->target() or ->target_index() for the same policy.
+ *
+ * If CPUFREQ_ENTRY_INVALID is returned by the driver's ->fast_switch()
+ * callback to indicate an error condition, the hardware configuration must be
+ * preserved.
+ */
+unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
+ unsigned int target_freq)
+{
+ clamp_val(target_freq, policy->min, policy->max);
+
+ return cpufreq_driver->fast_switch(policy, target_freq);
+}
+EXPORT_SYMBOL_GPL(cpufreq_driver_fast_switch);
+
/* Must set freqs->new to intermediate frequency */
static int __target_intermediate(struct cpufreq_policy *policy,
struct cpufreq_freqs *freqs, int index)
@@ -1946,6 +2060,12 @@
return ret ? ret : cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);
}
+static int cpufreq_exit_governor(struct cpufreq_policy *policy)
+{
+ cpufreq_disable_fast_switch(policy);
+ return cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
+}
+
int cpufreq_register_governor(struct cpufreq_governor *governor)
{
int err;
@@ -2101,7 +2221,7 @@
return ret;
}
- ret = cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
+ ret = cpufreq_exit_governor(policy);
if (ret) {
pr_err("%s: Failed to Exit Governor: %s (%d)\n",
__func__, old_gov->name, ret);
@@ -2118,7 +2238,7 @@
pr_debug("cpufreq: governor change\n");
return 0;
}
- cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
+ cpufreq_exit_governor(policy);
}
/* new governor failed, so re-start old one */