Commit b7898fda authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

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

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

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: default avatarRafael J. Wysocki <>
Acked-by: default avatarViresh Kumar <>
parent 379480d8
......@@ -458,6 +458,43 @@ static int acpi_cpufreq_target(struct cpufreq_policy *policy,
return result;
unsigned int acpi_cpufreq_fast_switch(struct cpufreq_policy *policy,
unsigned int target_freq)
struct acpi_cpufreq_data *data = policy->driver_data;
struct acpi_processor_performance *perf;
struct cpufreq_frequency_table *entry;
unsigned int next_perf_state, next_freq, freq;
* Find the closest frequency above target_freq.
* The table is sorted in the reverse order with respect to the
* frequency and all of the entries are valid (see the initialization).
entry = data->freq_table;
do {
freq = entry->frequency;
} while (freq >= target_freq && freq != CPUFREQ_TABLE_END);
next_freq = entry->frequency;
next_perf_state = entry->driver_data;
perf = to_perf_data(data);
if (perf->state == next_perf_state) {
if (unlikely(data->resume))
data->resume = 0;
return next_freq;
perf->state = next_perf_state;
return next_freq;
static unsigned long
acpi_cpufreq_guess_freq(struct acpi_cpufreq_data *data, unsigned int cpu)
......@@ -821,6 +858,9 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
data->resume = 1;
policy->fast_switch_possible = !acpi_pstate_strict &&
!(policy_is_shared(policy) && policy->shared_type != CPUFREQ_SHARED_TYPE_ANY);
return result;
......@@ -843,6 +883,7 @@ static int acpi_cpufreq_cpu_exit(struct cpufreq_policy *policy)
if (data) {
policy->fast_switch_possible = false;
policy->driver_data = NULL;
......@@ -876,6 +917,7 @@ static struct freq_attr *acpi_cpufreq_attr[] = {
static struct cpufreq_driver acpi_cpufreq_driver = {
.verify = cpufreq_generic_frequency_table_verify,
.target_index = acpi_cpufreq_target,
.fast_switch = acpi_cpufreq_fast_switch,
.bios_limit = acpi_processor_get_bios_limit,
.init = acpi_cpufreq_cpu_init,
.exit = acpi_cpufreq_cpu_exit,
......@@ -77,6 +77,7 @@ static inline bool has_target(void)
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 @@ void cpufreq_freq_transition_end(struct cpufreq_policy *policy,
* 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");
for (nb = cpufreq_transition_notifier_list.head; nb; nb = nb->next)
pr_info("%pF\n", nb->notifier_call);
* 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)
if (!policy->fast_switch_possible)
if (cpufreq_fast_switch_count >= 0) {
policy->fast_switch_enabled = true;
} else {
pr_warn("CPU%u: Fast frequency switching not enabled\n",
static void cpufreq_disable_fast_switch(struct cpufreq_policy *policy)
if (policy->fast_switch_enabled) {
policy->fast_switch_enabled = false;
if (!WARN_ON(cpufreq_fast_switch_count <= 0))
......@@ -1319,7 +1382,7 @@ static void cpufreq_offline(unsigned int cpu)
/* 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 @@ static unsigned int __cpufreq_get(struct cpufreq_policy *policy)
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 @@ int cpufreq_register_notifier(struct notifier_block *nb, unsigned int list)
switch (list) {
if (cpufreq_fast_switch_count > 0) {
return -EBUSY;
ret = srcu_notifier_chain_register(
&cpufreq_transition_notifier_list, nb);
if (!ret)
ret = blocking_notifier_chain_register(
......@@ -1706,8 +1783,14 @@ int cpufreq_unregister_notifier(struct notifier_block *nb, unsigned int list)
switch (list) {
ret = srcu_notifier_chain_unregister(
&cpufreq_transition_notifier_list, nb);
if (!ret && !WARN_ON(cpufreq_fast_switch_count >= 0))
ret = blocking_notifier_chain_unregister(
......@@ -1726,6 +1809,37 @@ EXPORT_SYMBOL(cpufreq_unregister_notifier);
* 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);
/* 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 @@ static int cpufreq_start_governor(struct cpufreq_policy *policy)
return ret ? ret : cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);
static int cpufreq_exit_governor(struct cpufreq_policy *policy)
return cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
int cpufreq_register_governor(struct cpufreq_governor *governor)
int err;
......@@ -2101,7 +2221,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
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 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
pr_debug("cpufreq: governor change\n");
return 0;
cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
/* new governor failed, so re-start old one */
......@@ -102,6 +102,17 @@ struct cpufreq_policy {
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_get_policy(struct cpufreq_policy *policy, unsigned int cpu);
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);
static inline unsigned int cpufreq_get(unsigned int cpu)
......@@ -236,6 +248,8 @@ struct cpufreq_driver {
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 @@ struct cpufreq_governor {
/* 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);
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