path: root/Documentation/cpu-freq/cpu-drivers.txt
diff options
Diffstat (limited to 'Documentation/cpu-freq/cpu-drivers.txt')
1 files changed, 27 insertions, 2 deletions
diff --git a/Documentation/cpu-freq/cpu-drivers.txt b/Documentation/cpu-freq/cpu-drivers.txt
index b045fe54986a..14f4e6336d88 100644
--- a/Documentation/cpu-freq/cpu-drivers.txt
+++ b/Documentation/cpu-freq/cpu-drivers.txt
@@ -26,6 +26,7 @@ Contents:
1.4 target/target_index or setpolicy?
1.5 target/target_index
1.6 setpolicy
+1.7 get_intermediate and target_intermediate
2. Frequency Table Helpers
@@ -79,6 +80,10 @@ cpufreq_driver.attr - A pointer to a NULL-terminated list of
"struct freq_attr" which allow to
export values to sysfs.
+and target_intermediate Used to switch to stable frequency while
+ changing CPU frequency.
1.2 Per-CPU Initialization
@@ -151,7 +156,7 @@ Some cpufreq-capable processors switch the frequency between certain
limits on their own. These shall use the ->setpolicy call
-1.4. target/target_index
+1.5. target/target_index
The target_index call has two arguments: struct cpufreq_policy *policy,
@@ -160,6 +165,9 @@ and unsigned int index (into the exposed frequency table).
The CPUfreq driver must set the new frequency when called here. The
actual frequency must be determined by freq_table[index].frequency.
+It should always restore to earlier frequency (i.e. policy->restore_freq) in
+case of errors, even if we switched to intermediate frequency earlier.
The target call has three arguments: struct cpufreq_policy *policy,
@@ -179,7 +187,7 @@ Here again the frequency table helper might assist you - see section 2
for details.
-1.5 setpolicy
+1.6 setpolicy
The setpolicy call only takes a struct cpufreq_policy *policy as
@@ -190,6 +198,23 @@ setting when policy->policy is CPUFREQ_POLICY_PERFORMANCE, and a
powersaving-oriented setting when CPUFREQ_POLICY_POWERSAVE. Also check
the reference implementation in drivers/cpufreq/longrun.c
+1.7 get_intermediate and target_intermediate
+Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION unset.
+get_intermediate should return a stable intermediate frequency platform wants to
+switch to, and target_intermediate() should set CPU to to that frequency, before
+jumping to the frequency corresponding to 'index'. Core will take care of
+sending notifications and driver doesn't have to handle them in
+target_intermediate() or target_index().
+Drivers can return '0' from get_intermediate() in case they don't wish to switch
+to intermediate frequency for some target frequency. In that case core will
+directly call ->target_index().
+NOTE: ->target_index() should restore to policy->restore_freq in case of
+failures as core would send notifications for that.
2. Frequency Table Helpers

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