cpufreq: Documentation: Updates based on current code

The cpufreq core has gone though lots of updates in recent times, but on
many occasions the documentation wasn't updated along with the code.
This patch tries to catchup the documentation with the code.

Also add Rafael and Viresh as the contributors to the documentation.

Based on a patch from Claudio Scordino.

Signed-off-by: Claudio Scordino <claudio@evidence.eu.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 99 insertions, 78 deletions

diff --git a/Documentation/cpu-freq/cpu-drivers.txt b/Documentation/cpu-freq/cpu-drivers.txt
index 772b94fde264..f71e6be26b83 100644
--- a/Documentation/cpu-freq/cpu-drivers.txt
+++ b/Documentation/cpu-freq/cpu-drivers.txt
@@ -9,6 +9,8 @@
 
 
 		    Dominik Brodowski  <linux@brodo.de>
+		Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+		   Viresh Kumar <viresh.kumar@linaro.org>
 
 
 
@@ -49,49 +51,65 @@ using cpufreq_register_driver()
 
 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.
 
@@ -117,47 +135,45 @@ policy->governor		must contain the "default policy" for
 				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).
@@ -186,9 +202,20 @@ actual frequency must be determined using the following rules:
 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
@@ -198,7 +225,7 @@ 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
+1.8 get_intermediate and target_intermediate
 --------------------------------------------
 
 Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION unset.
@@ -222,42 +249,36 @@ failures as core would send notifications for that.
 
 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.