forked from luck/tmp_suning_uos_patched
a0dd7b7965
CPUFreq specific helper functions for OPP (Operating Performance Points) now use generic OPP functions that allow CPUFreq to be be moved back into CPUFreq framework. This allows for independent modifications or future enhancements as needed isolated to just CPUFreq framework alone. Here, we just move relevant code and documentation to make this part of CPUFreq infrastructure. Cc: Kevin Hilman <khilman@deeprootsystems.com> Signed-off-by: Nishanth Menon <nm@ti.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
124 lines
4.2 KiB
Plaintext
124 lines
4.2 KiB
Plaintext
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>
|
|
|
|
|
|
|
|
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 is done by cpufreq_get_cpu and cpufreq_put_cpu,
|
|
which make sure that the cpufreq processor driver is correctly
|
|
registered with the core, and will not be unloaded until
|
|
cpufreq_put_cpu is called.
|
|
|
|
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 intended to be set. Each
|
|
CPUFreq policy notifier is called three times for a policy transition:
|
|
|
|
1.) During CPUFREQ_ADJUST all CPUFreq notifiers may change the limit if
|
|
they see a need for this - may it be thermal considerations or
|
|
hardware limitations.
|
|
|
|
2.) During CPUFREQ_INCOMPATIBLE only changes may be done in order to avoid
|
|
hardware failure.
|
|
|
|
3.) And during CPUFREQ_NOTIFY all notifiers are informed of the new policy
|
|
- if two hardware drivers failed to agree on a new policy before this
|
|
stage, the incompatible hardware shall be shut down, and the user
|
|
informed of this.
|
|
|
|
The phase is specified in the second argument to the notifier.
|
|
|
|
The third argument, a void *pointer, points to a struct cpufreq_policy
|
|
consisting of five values: cpu, min, max, policy and max_cpu_freq. min
|
|
and max are the lower and upper frequencies (in kHz) of the new
|
|
policy, policy the new policy, cpu the number of the affected CPU; and
|
|
max_cpu_freq the maximum supported CPU frequency. This value is given
|
|
for informational purposes only.
|
|
|
|
|
|
2.2 CPUFreq transition notifiers
|
|
--------------------------------
|
|
|
|
These are notified twice when the CPUfreq driver switches the CPU core
|
|
frequency and this change has 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
|
|
|
|
3. CPUFreq Table Generation with Operating Performance Point (OPP)
|
|
==================================================================
|
|
For details about OPP, see Documentation/power/opp.txt
|
|
|
|
dev_pm_opp_init_cpufreq_table - cpufreq framework typically is initialized with
|
|
cpufreq_frequency_table_cpuinfo which is provided with the list of
|
|
frequencies that are available for operation. 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)
|
|
cpufreq_frequency_table_cpuinfo(policy, 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
|