mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-22 20:23:57 +08:00
2dd0df8472
This isn't used anymore. Remove the helper and update documentation accordingly. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
296 lines
10 KiB
Plaintext
296 lines
10 KiB
Plaintext
CPU frequency and voltage scaling code in the Linux(TM) kernel
|
|
|
|
|
|
L i n u x C P U F r e q
|
|
|
|
C P U D r i v e r s
|
|
|
|
- information for developers -
|
|
|
|
|
|
Dominik Brodowski <linux@brodo.de>
|
|
Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
Viresh Kumar <viresh.kumar@linaro.org>
|
|
|
|
|
|
|
|
Clock scaling allows you to change the clock speed of the CPUs on the
|
|
fly. This is a nice method to save battery power, because the lower
|
|
the clock speed, the less power the CPU consumes.
|
|
|
|
|
|
Contents:
|
|
---------
|
|
1. What To Do?
|
|
1.1 Initialization
|
|
1.2 Per-CPU Initialization
|
|
1.3 verify
|
|
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
|
|
|
|
|
|
|
|
1. What To Do?
|
|
==============
|
|
|
|
So, you just got a brand-new CPU / chipset with datasheets and want to
|
|
add cpufreq support for this CPU / chipset? Great. Here are some hints
|
|
on what is necessary:
|
|
|
|
|
|
1.1 Initialization
|
|
------------------
|
|
|
|
First of all, in an __initcall level 7 (module_init()) or later
|
|
function check whether this kernel runs on the right CPU and the right
|
|
chipset. If so, register a struct cpufreq_driver with the CPUfreq core
|
|
using cpufreq_register_driver()
|
|
|
|
What shall this struct cpufreq_driver contain?
|
|
|
|
.name - The name of this driver.
|
|
|
|
.init - A pointer to the per-policy initialization function.
|
|
|
|
.verify - A pointer to a "verification" function.
|
|
|
|
.setpolicy _or_ .fast_switch _or_ .target _or_ .target_index - See
|
|
below on the differences.
|
|
|
|
And optionally
|
|
|
|
.flags - Hints for the cpufreq core.
|
|
|
|
.driver_data - cpufreq driver specific data.
|
|
|
|
.resolve_freq - Returns the most appropriate frequency for a target
|
|
frequency. Doesn't change the frequency though.
|
|
|
|
.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-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.
|
|
|
|
Then, the driver must fill in the following values:
|
|
|
|
policy->cpuinfo.min_freq _and_
|
|
policy->cpuinfo.max_freq - the minimum and maximum frequency
|
|
(in kHz) which is supported by
|
|
this CPU
|
|
policy->cpuinfo.transition_latency the time it takes on this CPU to
|
|
switch between two frequencies in
|
|
nanoseconds (if appropriate, else
|
|
specify CPUFREQ_ETERNAL)
|
|
|
|
policy->cur The current operating frequency of
|
|
this CPU (if appropriate)
|
|
policy->min,
|
|
policy->max,
|
|
policy->policy and, if necessary,
|
|
policy->governor must contain the "default policy" for
|
|
this CPU. A few moments later,
|
|
cpufreq_driver.verify and either
|
|
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.
|
|
|
|
|
|
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 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 or target_index or setpolicy or fast_switch?
|
|
-------------------------------------------------------
|
|
|
|
Most cpufreq drivers or even most cpu frequency scaling algorithms
|
|
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() 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).
|
|
|
|
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.
|
|
|
|
Deprecated:
|
|
----------
|
|
The target call has three arguments: struct cpufreq_policy *policy,
|
|
unsigned int target_frequency, unsigned int relation.
|
|
|
|
The CPUfreq driver must set the new frequency when called here. The
|
|
actual frequency must be determined using the following rules:
|
|
|
|
- keep close to "target_freq"
|
|
- policy->min <= new_freq <= policy->max (THIS MUST BE VALID!!!)
|
|
- if relation==CPUFREQ_REL_L, try to select a new_freq higher than or equal
|
|
target_freq. ("L for lowest, but no lower than")
|
|
- if relation==CPUFREQ_REL_H, try to select a new_freq lower than or equal
|
|
target_freq. ("H for highest, but no higher than")
|
|
|
|
Here again the frequency table helper might assist you - see section 2
|
|
for details.
|
|
|
|
1.6. fast_switch
|
|
----------------
|
|
|
|
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
|
|
in-chipset dynamic frequency switching to policy->min, the upper limit
|
|
to policy->max, and -if supported- select a performance-oriented
|
|
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
|
|
|
|
1.8 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 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
|
|
==========================
|
|
|
|
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 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.
|
|
|
|
The cpufreq table is verified automatically by the core if the policy contains a
|
|
valid pointer in its policy->freq_table field.
|
|
|
|
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,
|
|
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.
|
|
|
|
For example:
|
|
|
|
struct cpufreq_frequency_table *pos, *driver_freq_table;
|
|
|
|
cpufreq_for_each_entry(pos, driver_freq_table) {
|
|
/* Do something with pos */
|
|
pos->frequency = ...
|
|
}
|
|
|
|
If you need to work with the position of pos within driver_freq_table,
|
|
do not subtract the pointers, as it is quite costly. Instead, use the
|
|
macros cpufreq_for_each_entry_idx() and cpufreq_for_each_valid_entry_idx().
|