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there is no need for freq scaling as arm boost sets the freq and voltages itself.
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Documentation/cpu-freq/core.rst
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.. SPDX-License-Identifier: GPL-2.0
=============================================================
General description of the CPUFreq core and CPUFreq notifiers
=============================================================
Authors:
- Dominik Brodowski <linux@brodo.de>
- David Kimdon <dwhedon@debian.org>
- Rafael J. Wysocki <rafael.j.wysocki@intel.com>
- Viresh Kumar <viresh.kumar@linaro.org>
.. Contents:
1. CPUFreq core and interfaces
2. CPUFreq notifiers
3. CPUFreq Table Generation with Operating Performance Point (OPP)
1. General Information
======================
The CPUFreq core code is located in drivers/cpufreq/cpufreq.c. This
cpufreq code offers a standardized interface for the CPUFreq
architecture drivers (those pieces of code that do actual
frequency transitions), as well as to "notifiers". These are device
drivers or other part of the kernel that need to be informed of
policy changes (ex. thermal modules like ACPI) or of all
frequency changes (ex. timing code) or even need to force certain
speed limits (like LCD drivers on ARM architecture). Additionally, the
kernel "constant" loops_per_jiffy is updated on frequency changes
here.
Reference counting of the cpufreq policies is done by cpufreq_cpu_get
and cpufreq_cpu_put, which make sure that the cpufreq driver is
correctly registered with the core, and will not be unloaded until
cpufreq_put_cpu is called. That also ensures that the respective cpufreq
policy doesn't get freed while being used.
2. CPUFreq notifiers
====================
CPUFreq notifiers conform to the standard kernel notifier interface.
See linux/include/linux/notifier.h for details on notifiers.
There are two different CPUFreq notifiers - policy notifiers and
transition notifiers.
2.1 CPUFreq policy notifiers
----------------------------
These are notified when a new policy is created or removed.
The phase is specified in the second argument to the notifier. The phase is
CPUFREQ_CREATE_POLICY when the policy is first created and it is
CPUFREQ_REMOVE_POLICY when the policy is removed.
The third argument, a ``void *pointer``, points to a struct cpufreq_policy
consisting of several values, including min, max (the lower and upper
frequencies (in kHz) of the new policy).
2.2 CPUFreq transition notifiers
--------------------------------
These are notified twice for each online CPU in the policy, when the
CPUfreq driver switches the CPU core frequency and this change has no
any external implications.
The second argument specifies the phase - CPUFREQ_PRECHANGE or
CPUFREQ_POSTCHANGE.
The third argument is a struct cpufreq_freqs with the following
values:
====== ======================================
policy a pointer to the struct cpufreq_policy
old old frequency
new new frequency
flags flags of the cpufreq driver
====== ======================================
3. CPUFreq Table Generation with Operating Performance Point (OPP)
==================================================================
For details about OPP, see Documentation/power/opp.rst
dev_pm_opp_init_cpufreq_table -
This function provides a ready to use conversion routine to translate
the OPP layer's internal information about the available frequencies
into a format readily providable to cpufreq.
.. Warning::
Do not use this function in interrupt context.
Example::
soc_pm_init()
{
/* Do things */
r = dev_pm_opp_init_cpufreq_table(dev, &freq_table);
if (!r)
policy->freq_table = freq_table;
/* Do other things */
}
.. note::
This function is available only if CONFIG_CPU_FREQ is enabled in
addition to CONFIG_PM_OPP.
dev_pm_opp_free_cpufreq_table
Free up the table allocated by dev_pm_opp_init_cpufreq_table

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.. SPDX-License-Identifier: GPL-2.0
===============================================
How to Implement a new CPUFreq Processor Driver
===============================================
Authors:
- Dominik Brodowski <linux@brodo.de>
- Rafael J. Wysocki <rafael.j.wysocki@intel.com>
- Viresh Kumar <viresh.kumar@linaro.org>
.. 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.
.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.
.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().

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.. SPDX-License-Identifier: GPL-2.0
==========================================
General Description of sysfs CPUFreq Stats
==========================================
information for users
Author: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
.. Contents
1. Introduction
2. Statistics Provided (with example)
3. Configuring cpufreq-stats
1. Introduction
===============
cpufreq-stats is a driver that provides CPU frequency statistics for each CPU.
These statistics are provided in /sysfs as a bunch of read_only interfaces. This
interface (when configured) will appear in a separate directory under cpufreq
in /sysfs (<sysfs root>/devices/system/cpu/cpuX/cpufreq/stats/) for each CPU.
Various statistics will form read_only files under this directory.
This driver is designed to be independent of any particular cpufreq_driver
that may be running on your CPU. So, it will work with any cpufreq_driver.
2. Statistics Provided (with example)
=====================================
cpufreq stats provides following statistics (explained in detail below).
- time_in_state
- total_trans
- trans_table
All the statistics will be from the time the stats driver has been inserted
(or the time the stats were reset) to the time when a read of a particular
statistic is done. Obviously, stats driver will not have any information
about the frequency transitions before the stats driver insertion.
::
<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l
total 0
drwxr-xr-x 2 root root 0 May 14 16:06 .
drwxr-xr-x 3 root root 0 May 14 15:58 ..
--w------- 1 root root 4096 May 14 16:06 reset
-r--r--r-- 1 root root 4096 May 14 16:06 time_in_state
-r--r--r-- 1 root root 4096 May 14 16:06 total_trans
-r--r--r-- 1 root root 4096 May 14 16:06 trans_table
- **reset**
Write-only attribute that can be used to reset the stat counters. This can be
useful for evaluating system behaviour under different governors without the
need for a reboot.
- **time_in_state**
This gives the amount of time spent in each of the frequencies supported by
this CPU. The cat output will have "<frequency> <time>" pair in each line, which
will mean this CPU spent <time> usertime units of time at <frequency>. Output
will have one line for each of the supported frequencies. usertime units here
is 10mS (similar to other time exported in /proc).
::
<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state
3600000 2089
3400000 136
3200000 34
3000000 67
2800000 172488
- **total_trans**
This gives the total number of frequency transitions on this CPU. The cat
output will have a single count which is the total number of frequency
transitions.
::
<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans
20
- **trans_table**
This will give a fine grained information about all the CPU frequency
transitions. The cat output here is a two dimensional matrix, where an entry
<i,j> (row i, column j) represents the count of number of transitions from
Freq_i to Freq_j. Freq_i rows and Freq_j columns follow the sorting order in
which the driver has provided the frequency table initially to the cpufreq core
and so can be sorted (ascending or descending) or unsorted. The output here
also contains the actual freq values for each row and column for better
readability.
If the transition table is bigger than PAGE_SIZE, reading this will
return an -EFBIG error.
::
<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table
From : To
: 3600000 3400000 3200000 3000000 2800000
3600000: 0 5 0 0 0
3400000: 4 0 2 0 0
3200000: 0 1 0 2 0
3000000: 0 0 1 0 3
2800000: 0 0 0 2 0
3. Configuring cpufreq-stats
============================
To configure cpufreq-stats in your kernel::
Config Main Menu
Power management options (ACPI, APM) --->
CPU Frequency scaling --->
[*] CPU Frequency scaling
[*] CPU frequency translation statistics
"CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure
cpufreq-stats.
"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the
statistics which includes time_in_state, total_trans and trans_table.
Once this option is enabled and your CPU supports cpufrequency, you
will be able to see the CPU frequency statistics in /sysfs.

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.. SPDX-License-Identifier: GPL-2.0
==============================================================================
Linux CPUFreq - CPU frequency and voltage scaling code in the Linux(TM) kernel
==============================================================================
Author: Dominik Brodowski <linux@brodo.de>
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.
.. toctree::
:maxdepth: 1
core
cpu-drivers
cpufreq-stats
Mailing List
------------
There is a CPU frequency changing CVS commit and general list where
you can report bugs, problems or submit patches. To post a message,
send an email to linux-pm@vger.kernel.org.
Links
-----
the FTP archives:
* ftp://ftp.linux.org.uk/pub/linux/cpufreq/
how to access the CVS repository:
* http://cvs.arm.linux.org.uk/
the CPUFreq Mailing list:
* http://vger.kernel.org/vger-lists.html#linux-pm
Clock and voltage scaling for the SA-1100:
* http://www.lartmaker.nl/projects/scaling