From 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sat, 27 Apr 2024 12:05:51 +0200 Subject: Adding upstream version 5.10.209. Signed-off-by: Daniel Baumann --- Documentation/arm/samsung-s3c24xx/cpufreq.rst | 76 +++++++++++++++++++++++++++ 1 file changed, 76 insertions(+) create mode 100644 Documentation/arm/samsung-s3c24xx/cpufreq.rst (limited to 'Documentation/arm/samsung-s3c24xx/cpufreq.rst') diff --git a/Documentation/arm/samsung-s3c24xx/cpufreq.rst b/Documentation/arm/samsung-s3c24xx/cpufreq.rst new file mode 100644 index 000000000..2ddc26c03 --- /dev/null +++ b/Documentation/arm/samsung-s3c24xx/cpufreq.rst @@ -0,0 +1,76 @@ +======================= +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 separate PLL and clock divider for the + ARM core is available as a separate 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 -- cgit v1.2.3