Re: [PATCH v2 4/4] clk: dt: Introduce always-on clock domain documentation

From: Geert Uytterhoeven
Date: Thu Feb 19 2015 - 04:55:27 EST

Hi Lee,

On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@xxxxxxxxxx> wrote:
>> What kind of clocks are these? What do they control?
>> Memory controllers? Bus controllers?
>> They must control some device(s), so there should be one or more device
>> nodes in DT that reference these clocks.
>> As soon as that information is in DT, support can be added to Linux to
>> make sure the "critical" clocks stay enabled, either through a real driver,
>> or through platform code.
> Some do, some don't. For instance, we have one clock which controls
> SPI and I2C that must not be turned off. We discovered this then when
> a suspend was attempted and the board refused to resume. This clock
> also runs one of the critical interconnects that runs from the a9. It
> would be wrong to remove the clk_disable() attempt from the SPI/I2C
> drivers because the same IP on another board might be controlled by a
> different clock which is able to be gated.
> There are also clocks which control other interconnects that are not
> connected to any device drivers. If we fail to take references for
> them before clk_disable_unused() is called, again the board hangs. We
> even lose JTAG support.

Interconnects are buses. Can't you represent those buses in the DT
hierarchy, and give them clocks properties?



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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