+++ /dev/null
- 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 F r e q C o r e
-
-
- Dominik Brodowski <linux@brodo.de>
- David Kimdon <dwhedon@debian.org>
- 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. 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:
-cpu - number of the affected CPU
-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
projects / linux-2.6-block.git / blobdiff