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113 lines
3.6 KiB
113 lines
3.6 KiB
.. 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 <[email protected]> |
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- David Kimdon <[email protected]> |
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- Rafael J. Wysocki <[email protected]> |
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- Viresh Kumar <[email protected]> |
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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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