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| author | Emilio López <emilio@elopez.com.ar> | 2013-02-25 11:44:28 -0300 |
|---|---|---|
| committer | Mike Turquette <mturquette@linaro.org> | 2013-03-27 08:35:34 -0700 |
| commit | 8eb896ab7a716308698de77073a9265f584b12fc (patch) | |
| tree | 4a62ae92f2287d77fb6b43028063b26b96a24455 /Documentation/arm | |
| parent | e874a6697710f52fa8ab29487a99034d5d96fdcc (diff) | |
| download | linux-8eb896ab7a716308698de77073a9265f584b12fc.tar.gz linux-8eb896ab7a716308698de77073a9265f584b12fc.tar.bz2 linux-8eb896ab7a716308698de77073a9265f584b12fc.zip | |
arm: sunxi: Add useful information about sunxi clocks
This patch contains useful bits of information about the sunxi clocks
that may help and/or be interesting for current and future developers.
Signed-off-by: Emilio López <emilio@elopez.com.ar>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
Diffstat (limited to 'Documentation/arm')
| -rw-r--r-- | Documentation/arm/sunxi/clocks.txt | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/Documentation/arm/sunxi/clocks.txt b/Documentation/arm/sunxi/clocks.txt new file mode 100644 index 000000000000..e09a88aa3136 --- /dev/null +++ b/Documentation/arm/sunxi/clocks.txt @@ -0,0 +1,56 @@ +Frequently asked questions about the sunxi clock system +======================================================= + +This document contains useful bits of information that people tend to ask +about the sunxi clock system, as well as accompanying ASCII art when adequate. + +Q: Why is the main 24MHz oscillator gatable? Wouldn't that break the + system? + +A: The 24MHz oscillator allows gating to save power. Indeed, if gated + carelessly the system would stop functioning, but with the right + steps, one can gate it and keep the system running. Consider this + simplified suspend example: + + While the system is operational, you would see something like + + 24MHz 32kHz + | + PLL1 + \ + \_ CPU Mux + | + [CPU] + + When you are about to suspend, you switch the CPU Mux to the 32kHz + oscillator: + + 24Mhz 32kHz + | | + PLL1 | + / + CPU Mux _/ + | + [CPU] + + Finally you can gate the main oscillator + + 32kHz + | + | + / + CPU Mux _/ + | + [CPU] + +Q: Were can I learn more about the sunxi clocks? + +A: The linux-sunxi wiki contains a page documenting the clock registers, + you can find it at + + http://linux-sunxi.org/A10/CCM + + The authoritative source for information at this time is the ccmu driver + released by Allwinner, you can find it at + + https://github.com/linux-sunxi/linux-sunxi/tree/sunxi-3.0/arch/arm/mach-sun4i/clock/ccmu |