diff options
Diffstat (limited to 'Documentation/cpu-freq/core.txt')
| -rw-r--r-- | Documentation/cpu-freq/core.txt | 98 |
1 files changed, 0 insertions, 98 deletions
diff --git a/Documentation/cpu-freq/core.txt b/Documentation/cpu-freq/core.txt deleted file mode 100644 index ce0666e51036..000000000000 --- a/Documentation/cpu-freq/core.txt +++ /dev/null @@ -1,98 +0,0 @@ - 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 - -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 - -If the cpufreq core detects the frequency has changed while the system -was suspended, these notifiers are called with CPUFREQ_RESUMECHANGE as -second argument. |