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