Dominik Brodowski <linux@brodo.de>
+ Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+ Viresh Kumar <viresh.kumar@linaro.org>
What shall this struct cpufreq_driver contain?
-cpufreq_driver.name - The name of this driver.
+ .name - The name of this driver.
-cpufreq_driver.init - A pointer to the per-CPU initialization
- function.
+ .init - A pointer to the per-policy initialization function.
-cpufreq_driver.verify - A pointer to a "verification" function.
+ .verify - A pointer to a "verification" function.
-cpufreq_driver.setpolicy _or_
-cpufreq_driver.target/
-target_index - See below on the differences.
+ .setpolicy _or_ .fast_switch _or_ .target _or_ .target_index - See
+ below on the differences.
And optionally
-cpufreq_driver.exit - A pointer to a per-CPU cleanup
- function called during CPU_POST_DEAD
- phase of cpu hotplug process.
+ .flags - Hints for the cpufreq core.
-cpufreq_driver.stop_cpu - A pointer to a per-CPU stop function
- called during CPU_DOWN_PREPARE phase of
- cpu hotplug process.
+ .driver_data - cpufreq driver specific data.
-cpufreq_driver.resume - A pointer to a per-CPU resume function
- which is called with interrupts disabled
- and _before_ the pre-suspend frequency
- and/or policy is restored by a call to
- ->target/target_index or ->setpolicy.
+ .resolve_freq - Returns the most appropriate frequency for a target
+ frequency. Doesn't change the frequency though.
-cpufreq_driver.attr - A pointer to a NULL-terminated list of
- "struct freq_attr" which allow to
- export values to sysfs.
+ .get_intermediate and target_intermediate - Used to switch to stable
+ frequency while changing CPU frequency.
-cpufreq_driver.get_intermediate
-and target_intermediate Used to switch to stable frequency while
- changing CPU frequency.
+ .get - Returns current frequency of the CPU.
+
+ .bios_limit - Returns HW/BIOS max frequency limitations for the CPU.
+
+ .exit - A pointer to a per-policy cleanup function called during
+ CPU_POST_DEAD phase of cpu hotplug process.
+
+ .stop_cpu - A pointer to a per-policy stop function called during
+ CPU_DOWN_PREPARE phase of cpu hotplug process.
+
+ .suspend - A pointer to a per-policy suspend function which is called
+ with interrupts disabled and _after_ the governor is stopped for the
+ policy.
+
+ .resume - A pointer to a per-policy resume function which is called
+ with interrupts disabled and _before_ the governor is started again.
+
+ .ready - A pointer to a per-policy ready function which is called after
+ the policy is fully initialized.
+
+ .attr - A pointer to a NULL-terminated list of "struct freq_attr" which
+ allow to export values to sysfs.
+
+ .boost_enabled - If set, boost frequencies are enabled.
+
+ .set_boost - A pointer to a per-policy function to enable/disable boost
+ frequencies.
1.2 Per-CPU Initialization
--------------------------
Whenever a new CPU is registered with the device model, or after the
-cpufreq driver registers itself, the per-CPU initialization function
-cpufreq_driver.init is called. It takes a struct cpufreq_policy
-*policy as argument. What to do now?
+cpufreq driver registers itself, the per-policy initialization function
+cpufreq_driver.init is called if no cpufreq policy existed for the CPU.
+Note that the .init() and .exit() routines are called only once for the
+policy and not for each CPU managed by the policy. It takes a struct
+cpufreq_policy *policy as argument. What to do now?
If necessary, activate the CPUfreq support on your CPU.
cpufreq_driver.setpolicy or
cpufreq_driver.target/target_index is called
with these values.
+policy->cpus Update this with the masks of the
+ (online + offline) CPUs that do DVFS
+ along with this CPU (i.e. that share
+ clock/voltage rails with it).
For setting some of these values (cpuinfo.min[max]_freq, policy->min[max]), the
frequency table helpers might be helpful. See the section 2 for more information
on them.
-SMP systems normally have same clock source for a group of cpus. For these the
-.init() would be called only once for the first online cpu. Here the .init()
-routine must initialize policy->cpus with mask of all possible cpus (Online +
-Offline) that share the clock. Then the core would copy this mask onto
-policy->related_cpus and will reset policy->cpus to carry only online cpus.
-
1.3 verify
-------------
+----------
When the user decides a new policy (consisting of
"policy,governor,min,max") shall be set, this policy must be validated
so that incompatible values can be corrected. For verifying these
-values, a frequency table helper and/or the
-cpufreq_verify_within_limits(struct cpufreq_policy *policy, unsigned
-int min_freq, unsigned int max_freq) function might be helpful. See
-section 2 for details on frequency table helpers.
+values cpufreq_verify_within_limits(struct cpufreq_policy *policy,
+unsigned int min_freq, unsigned int max_freq) function might be helpful.
+See section 2 for details on frequency table helpers.
You need to make sure that at least one valid frequency (or operating
range) is within policy->min and policy->max. If necessary, increase
policy->max first, and only if this is no solution, decrease policy->min.
-1.4 target/target_index or setpolicy?
-----------------------------
+1.4 target or target_index or setpolicy or fast_switch?
+-------------------------------------------------------
Most cpufreq drivers or even most cpu frequency scaling algorithms
-only allow the CPU to be set to one frequency. For these, you use the
-->target/target_index call.
+only allow the CPU frequency to be set to predefined fixed values. For
+these, you use the ->target(), ->target_index() or ->fast_switch()
+callbacks.
-Some cpufreq-capable processors switch the frequency between certain
-limits on their own. These shall use the ->setpolicy call
+Some cpufreq capable processors switch the frequency between certain
+limits on their own. These shall use the ->setpolicy() callback.
1.5. target/target_index
--------------
+------------------------
The target_index call has two arguments: struct cpufreq_policy *policy,
and unsigned int index (into the exposed frequency table).
Here again the frequency table helper might assist you - see section 2
for details.
+1.6. fast_switch
+----------------
-1.6 setpolicy
----------------
+This function is used for frequency switching from scheduler's context.
+Not all drivers are expected to implement it, as sleeping from within
+this callback isn't allowed. This callback must be highly optimized to
+do switching as fast as possible.
+
+This function has two arguments: struct cpufreq_policy *policy and
+unsigned int target_frequency.
+
+
+1.7 setpolicy
+-------------
The setpolicy call only takes a struct cpufreq_policy *policy as
argument. You need to set the lower limit of the in-processor or
powersaving-oriented setting when CPUFREQ_POLICY_POWERSAVE. Also check
the reference implementation in drivers/cpufreq/longrun.c
-1.7 get_intermediate and target_intermediate
+1.8 get_intermediate and target_intermediate
--------------------------------------------
Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION unset.
As most cpufreq processors only allow for being set to a few specific
frequencies, a "frequency table" with some functions might assist in
-some work of the processor driver. Such a "frequency table" consists
-of an array of struct cpufreq_frequency_table entries, with any value in
-"driver_data" you want to use, and the corresponding frequency in
-"frequency". At the end of the table, you need to add a
-cpufreq_frequency_table entry with frequency set to CPUFREQ_TABLE_END. And
-if you want to skip one entry in the table, set the frequency to
-CPUFREQ_ENTRY_INVALID. The entries don't need to be in ascending
-order.
-
-By calling cpufreq_table_validate_and_show(struct cpufreq_policy *policy,
- struct cpufreq_frequency_table *table);
-the cpuinfo.min_freq and cpuinfo.max_freq values are detected, and
-policy->min and policy->max are set to the same values. This is
-helpful for the per-CPU initialization stage.
-
-int cpufreq_frequency_table_verify(struct cpufreq_policy *policy,
- struct cpufreq_frequency_table *table);
-assures that at least one valid frequency is within policy->min and
-policy->max, and all other criteria are met. This is helpful for the
-->verify call.
-
-int cpufreq_frequency_table_target(struct cpufreq_policy *policy,
- unsigned int target_freq,
- unsigned int relation);
-
-is the corresponding frequency table helper for the ->target
-stage. Just pass the values to this function, and this function
-returns the number of the frequency table entry which contains
-the frequency the CPU shall be set to.
+some work of the processor driver. Such a "frequency table" consists of
+an array of struct cpufreq_frequency_table entries, with driver specific
+values in "driver_data", the corresponding frequency in "frequency" and
+flags set. At the end of the table, you need to add a
+cpufreq_frequency_table entry with frequency set to CPUFREQ_TABLE_END.
+And if you want to skip one entry in the table, set the frequency to
+CPUFREQ_ENTRY_INVALID. The entries don't need to be in sorted in any
+particular order, but if they are cpufreq core will do DVFS a bit
+quickly for them as search for best match is faster.
+
+By calling cpufreq_table_validate_and_show(), the cpuinfo.min_freq and
+cpuinfo.max_freq values are detected, and policy->min and policy->max
+are set to the same values. This is helpful for the per-CPU
+initialization stage.
+
+cpufreq_frequency_table_verify() assures that at least one valid
+frequency is within policy->min and policy->max, and all other criteria
+are met. This is helpful for the ->verify call.
+
+cpufreq_frequency_table_target() is the corresponding frequency table
+helper for the ->target stage. Just pass the values to this function,
+and this function returns the of the frequency table entry which
+contains the frequency the CPU shall be set to.
The following macros can be used as iterators over cpufreq_frequency_table:
cpufreq_for_each_entry(pos, table) - iterates over all entries of frequency
table.
-cpufreq-for_each_valid_entry(pos, table) - iterates over all entries,
+cpufreq_for_each_valid_entry(pos, table) - iterates over all entries,
excluding CPUFREQ_ENTRY_INVALID frequencies.
Use arguments "pos" - a cpufreq_frequency_table * as a loop cursor and
"table" - the cpufreq_frequency_table * you want to iterate over.
projects / linux.git / blobdiff