forked from luck/tmp_suning_uos_patched
docs: cpu-freq: convert cpu-drivers.txt to ReST
- Add a SPDX header; - Add a document title, based on the original contents of cpu-freq/index.txt; - Use lists where needed; - Comment out the existing text-only index; - Adjust some title marks; - Add table markups; - Add notes markups; - Mark literal blocks as such; - use ``foo`` for literal texts; - Some whitespace fixes and new line breaks; - Add it to cpu-freq/index.rst. Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Mauro Carvalho Chehab
Rafael J. Wysocki
parent
c460f972d3
commit
8f92058987
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@ -1,35 +1,27 @@
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CPU frequency and voltage scaling code in the Linux(TM) kernel
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.. SPDX-License-Identifier: GPL-2.0
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===============================================
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How to Implement a new CPUFreq Processor Driver
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===============================================
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Authors:
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L i n u x C P U F r e q
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- Dominik Brodowski <linux@brodo.de>
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- Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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- Viresh Kumar <viresh.kumar@linaro.org>
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C P U D r i v e r s
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.. Contents
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- information for developers -
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Dominik Brodowski <linux@brodo.de>
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Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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Viresh Kumar <viresh.kumar@linaro.org>
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Clock scaling allows you to change the clock speed of the CPUs on the
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fly. This is a nice method to save battery power, because the lower
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the clock speed, the less power the CPU consumes.
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Contents:
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---------
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1. What To Do?
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1.1 Initialization
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1.2 Per-CPU Initialization
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1.3 verify
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1.4 target/target_index or setpolicy?
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1.5 target/target_index
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1.6 setpolicy
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1.7 get_intermediate and target_intermediate
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2. Frequency Table Helpers
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1. What To Do?
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1.1 Initialization
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1.2 Per-CPU Initialization
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1.3 verify
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1.4 target/target_index or setpolicy?
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1.5 target/target_index
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1.6 setpolicy
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1.7 get_intermediate and target_intermediate
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2. Frequency Table Helpers
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@ -49,7 +41,7 @@ function check whether this kernel runs on the right CPU and the right
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chipset. If so, register a struct cpufreq_driver with the CPUfreq core
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using cpufreq_register_driver()
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What shall this struct cpufreq_driver contain?
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What shall this struct cpufreq_driver contain?
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.name - The name of this driver.
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@ -108,37 +100,42 @@ Whenever a new CPU is registered with the device model, or after the
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cpufreq driver registers itself, the per-policy initialization function
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cpufreq_driver.init is called if no cpufreq policy existed for the CPU.
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Note that the .init() and .exit() routines are called only once for the
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policy and not for each CPU managed by the policy. It takes a struct
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cpufreq_policy *policy as argument. What to do now?
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policy and not for each CPU managed by the policy. It takes a ``struct
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cpufreq_policy *policy`` as argument. What to do now?
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If necessary, activate the CPUfreq support on your CPU.
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Then, the driver must fill in the following values:
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policy->cpuinfo.min_freq _and_
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policy->cpuinfo.max_freq - the minimum and maximum frequency
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(in kHz) which is supported by
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this CPU
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policy->cpuinfo.transition_latency the time it takes on this CPU to
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switch between two frequencies in
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nanoseconds (if appropriate, else
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specify CPUFREQ_ETERNAL)
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policy->cur The current operating frequency of
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this CPU (if appropriate)
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policy->min,
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policy->max,
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policy->policy and, if necessary,
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policy->governor must contain the "default policy" for
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this CPU. A few moments later,
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cpufreq_driver.verify and either
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cpufreq_driver.setpolicy or
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cpufreq_driver.target/target_index is called
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with these values.
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policy->cpus Update this with the masks of the
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(online + offline) CPUs that do DVFS
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along with this CPU (i.e. that share
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clock/voltage rails with it).
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+-----------------------------------+--------------------------------------+
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|policy->cpuinfo.min_freq _and_ | |
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|policy->cpuinfo.max_freq | the minimum and maximum frequency |
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| | (in kHz) which is supported by |
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| | this CPU |
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+-----------------------------------+--------------------------------------+
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|policy->cpuinfo.transition_latency | the time it takes on this CPU to |
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| | switch between two frequencies in |
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| | nanoseconds (if appropriate, else |
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| | specify CPUFREQ_ETERNAL) |
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+-----------------------------------+--------------------------------------+
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|policy->cur | The current operating frequency of |
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| | this CPU (if appropriate) |
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+-----------------------------------+--------------------------------------+
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|policy->min, | |
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|policy->max, | |
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|policy->policy and, if necessary, | |
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|policy->governor | must contain the "default policy" for|
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| | this CPU. A few moments later, |
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| | cpufreq_driver.verify and either |
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| | cpufreq_driver.setpolicy or |
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| | cpufreq_driver.target/target_index is|
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| | called with these values. |
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+-----------------------------------+--------------------------------------+
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|policy->cpus | Update this with the masks of the |
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| | (online + offline) CPUs that do DVFS |
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| | along with this CPU (i.e. that share|
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| | clock/voltage rails with it). |
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+-----------------------------------+--------------------------------------+
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For setting some of these values (cpuinfo.min[max]_freq, policy->min[max]), the
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frequency table helpers might be helpful. See the section 2 for more information
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@ -151,8 +148,8 @@ on them.
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When the user decides a new policy (consisting of
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"policy,governor,min,max") shall be set, this policy must be validated
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so that incompatible values can be corrected. For verifying these
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values cpufreq_verify_within_limits(struct cpufreq_policy *policy,
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unsigned int min_freq, unsigned int max_freq) function might be helpful.
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values cpufreq_verify_within_limits(``struct cpufreq_policy *policy``,
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``unsigned int min_freq``, ``unsigned int max_freq``) function might be helpful.
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See section 2 for details on frequency table helpers.
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You need to make sure that at least one valid frequency (or operating
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@ -163,7 +160,7 @@ policy->max first, and only if this is no solution, decrease policy->min.
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1.4 target or target_index or setpolicy or fast_switch?
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-------------------------------------------------------
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Most cpufreq drivers or even most cpu frequency scaling algorithms
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Most cpufreq drivers or even most cpu frequency scaling algorithms
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only allow the CPU frequency to be set to predefined fixed values. For
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these, you use the ->target(), ->target_index() or ->fast_switch()
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callbacks.
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@ -175,8 +172,8 @@ limits on their own. These shall use the ->setpolicy() callback.
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1.5. target/target_index
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------------------------
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The target_index call has two arguments: struct cpufreq_policy *policy,
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and unsigned int index (into the exposed frequency table).
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The target_index call has two arguments: ``struct cpufreq_policy *policy``,
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and ``unsigned int`` index (into the exposed frequency table).
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The CPUfreq driver must set the new frequency when called here. The
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actual frequency must be determined by freq_table[index].frequency.
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@ -184,9 +181,9 @@ actual frequency must be determined by freq_table[index].frequency.
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It should always restore to earlier frequency (i.e. policy->restore_freq) in
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case of errors, even if we switched to intermediate frequency earlier.
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Deprecated:
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Deprecated
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----------
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The target call has three arguments: struct cpufreq_policy *policy,
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The target call has three arguments: ``struct cpufreq_policy *policy``,
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unsigned int target_frequency, unsigned int relation.
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The CPUfreq driver must set the new frequency when called here. The
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@ -210,14 +207,14 @@ Not all drivers are expected to implement it, as sleeping from within
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this callback isn't allowed. This callback must be highly optimized to
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do switching as fast as possible.
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This function has two arguments: struct cpufreq_policy *policy and
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unsigned int target_frequency.
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This function has two arguments: ``struct cpufreq_policy *policy`` and
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``unsigned int target_frequency``.
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1.7 setpolicy
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-------------
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The setpolicy call only takes a struct cpufreq_policy *policy as
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The setpolicy call only takes a ``struct cpufreq_policy *policy`` as
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argument. You need to set the lower limit of the in-processor or
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in-chipset dynamic frequency switching to policy->min, the upper limit
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to policy->max, and -if supported- select a performance-oriented
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@ -278,10 +275,10 @@ table.
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cpufreq_for_each_valid_entry(pos, table) - iterates over all entries,
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excluding CPUFREQ_ENTRY_INVALID frequencies.
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Use arguments "pos" - a cpufreq_frequency_table * as a loop cursor and
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"table" - the cpufreq_frequency_table * you want to iterate over.
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Use arguments "pos" - a ``cpufreq_frequency_table *`` as a loop cursor and
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"table" - the ``cpufreq_frequency_table *`` you want to iterate over.
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For example:
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For example::
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struct cpufreq_frequency_table *pos, *driver_freq_table;
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@ -15,6 +15,7 @@ Author: Dominik Brodowski <linux@brodo.de>
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:maxdepth: 1
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core
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cpu-drivers
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Mailing List
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------------
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