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author | Paul Mundt <lethal@linux-sh.org> | 2009-09-16 13:48:32 +0900 |
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committer | Paul Mundt <lethal@linux-sh.org> | 2009-09-16 13:48:32 +0900 |
commit | ea88023b3491a384575ebcd5e8a449e841a28a24 (patch) | |
tree | f46e3d8302e44dc55ce31823501e100472d29683 /Documentation/arm/Samsung-S3C24XX/CPUfreq.txt | |
parent | a6f15ade97989d414e9bf33874c9d5d1f39808ec (diff) | |
parent | 0cb583fd2862f19ea88b02eb307d11c09e51e2f8 (diff) |
Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
Conflicts:
arch/sh/kernel/vmlinux.lds.S
Diffstat (limited to 'Documentation/arm/Samsung-S3C24XX/CPUfreq.txt')
-rw-r--r-- | Documentation/arm/Samsung-S3C24XX/CPUfreq.txt | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/Documentation/arm/Samsung-S3C24XX/CPUfreq.txt b/Documentation/arm/Samsung-S3C24XX/CPUfreq.txt new file mode 100644 index 00000000000..76b3a11e90b --- /dev/null +++ b/Documentation/arm/Samsung-S3C24XX/CPUfreq.txt @@ -0,0 +1,75 @@ + S3C24XX CPUfreq support + ======================= + +Introduction +------------ + + The S3C24XX series support a number of power saving systems, such as + the ability to change the core, memory and peripheral operating + frequencies. The core control is exported via the CPUFreq driver + which has a number of different manual or automatic controls over the + rate the core is running at. + + There are two forms of the driver depending on the specific CPU and + how the clocks are arranged. The first implementation used as single + PLL to feed the ARM, memory and peripherals via a series of dividers + and muxes and this is the implementation that is documented here. A + newer version where there is a seperate PLL and clock divider for the + ARM core is available as a seperate driver. + + +Layout +------ + + The code core manages the CPU specific drivers, any data that they + need to register and the interface to the generic drivers/cpufreq + system. Each CPU registers a driver to control the PLL, clock dividers + and anything else associated with it. Any board that wants to use this + framework needs to supply at least basic details of what is required. + + The core registers with drivers/cpufreq at init time if all the data + necessary has been supplied. + + +CPU support +----------- + + The support for each CPU depends on the facilities provided by the + SoC and the driver as each device has different PLL and clock chains + associated with it. + + +Slow Mode +--------- + + The SLOW mode where the PLL is turned off altogether and the + system is fed by the external crystal input is currently not + supported. + + +sysfs +----- + + The core code exports extra information via sysfs in the directory + devices/system/cpu/cpu0/arch-freq. + + +Board Support +------------- + + Each board that wants to use the cpufreq code must register some basic + information with the core driver to provide information about what the + board requires and any restrictions being placed on it. + + The board needs to supply information about whether it needs the IO bank + timings changing, any maximum frequency limits and information about the + SDRAM refresh rate. + + + + +Document Author +--------------- + +Ben Dooks, Copyright 2009 Simtec Electronics +Licensed under GPLv2 |