ARM: S3C: CPUFREQ: Add documentation for system

Add documentation for the S3C24XX style CPUFREQ driver.

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

1 files changed, 75 insertions, 0 deletions

diff --git a/Documentation/arm/Samsung-S3C24XX/CPUfreq.txt b/Documentation/arm/Samsung-S3C24XX/CPUfreq.txt
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+                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