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author | Russell King <rmk@dyn-67.arm.linux.org.uk> | 2009-09-12 07:02:26 -0400 |
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committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2009-09-12 07:02:26 -0400 |
commit | ddd559b13f6d2fe3ad68c4b3f5235fd3c2eae4e3 (patch) | |
tree | d827bca3fc825a0ac33efbcd493713be40fcc812 /Documentation/arm | |
parent | cf7a2b4fb6a9b86779930a0a123b0df41aa9208f (diff) | |
parent | f17a1f06d2fa93f4825be572622eb02c4894db4e (diff) |
Merge branch 'devel-stable' into devel
Conflicts:
MAINTAINERS
arch/arm/mm/fault.c
Diffstat (limited to 'Documentation/arm')
-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 000000000000..76b3a11e90be --- /dev/null +++ b/Documentation/arm/Samsung-S3C24XX/CPUfreq.txt | |||
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1 | S3C24XX CPUfreq support | ||
2 | ======================= | ||
3 | |||
4 | Introduction | ||
5 | ------------ | ||
6 | |||
7 | The S3C24XX series support a number of power saving systems, such as | ||
8 | the ability to change the core, memory and peripheral operating | ||
9 | frequencies. The core control is exported via the CPUFreq driver | ||
10 | which has a number of different manual or automatic controls over the | ||
11 | rate the core is running at. | ||
12 | |||
13 | There are two forms of the driver depending on the specific CPU and | ||
14 | how the clocks are arranged. The first implementation used as single | ||
15 | PLL to feed the ARM, memory and peripherals via a series of dividers | ||
16 | and muxes and this is the implementation that is documented here. A | ||
17 | newer version where there is a seperate PLL and clock divider for the | ||
18 | ARM core is available as a seperate driver. | ||
19 | |||
20 | |||
21 | Layout | ||
22 | ------ | ||
23 | |||
24 | The code core manages the CPU specific drivers, any data that they | ||
25 | need to register and the interface to the generic drivers/cpufreq | ||
26 | system. Each CPU registers a driver to control the PLL, clock dividers | ||
27 | and anything else associated with it. Any board that wants to use this | ||
28 | framework needs to supply at least basic details of what is required. | ||
29 | |||
30 | The core registers with drivers/cpufreq at init time if all the data | ||
31 | necessary has been supplied. | ||
32 | |||
33 | |||
34 | CPU support | ||
35 | ----------- | ||
36 | |||
37 | The support for each CPU depends on the facilities provided by the | ||
38 | SoC and the driver as each device has different PLL and clock chains | ||
39 | associated with it. | ||
40 | |||
41 | |||
42 | Slow Mode | ||
43 | --------- | ||
44 | |||
45 | The SLOW mode where the PLL is turned off altogether and the | ||
46 | system is fed by the external crystal input is currently not | ||
47 | supported. | ||
48 | |||
49 | |||
50 | sysfs | ||
51 | ----- | ||
52 | |||
53 | The core code exports extra information via sysfs in the directory | ||
54 | devices/system/cpu/cpu0/arch-freq. | ||
55 | |||
56 | |||
57 | Board Support | ||
58 | ------------- | ||
59 | |||
60 | Each board that wants to use the cpufreq code must register some basic | ||
61 | information with the core driver to provide information about what the | ||
62 | board requires and any restrictions being placed on it. | ||
63 | |||
64 | The board needs to supply information about whether it needs the IO bank | ||
65 | timings changing, any maximum frequency limits and information about the | ||
66 | SDRAM refresh rate. | ||
67 | |||
68 | |||
69 | |||
70 | |||
71 | Document Author | ||
72 | --------------- | ||
73 | |||
74 | Ben Dooks, Copyright 2009 Simtec Electronics | ||
75 | Licensed under GPLv2 | ||