Re: [PATCH v5 00/11] PM / Domains: Generic OF-based support

Geert Uytterhoeven
2014-09-26T10:01:17Z

Hi Thierry,

On Fri, Sep 26, 2014 at 11:56 AM, Thierry Reding
<thierry.reding@gmail.com> wrote:
>> > An alternative would be to make the power-domain controller look up the
>> > clock within the user's device tree node. That could be problematic,
>> > because while the module clock is always the first clock in current
>> > device trees, there aren't ordering guarantees, so we'd have to rely on
>> > the clock name.
>>
>> Or on some other way.
>> Do you have a separate hardware block that controls all (and only) the
>> module clocks?
>
> No, the "clock and reset controller" controls all clocks (and resets) on
> the SoC.

Sorry, with "only the module clocks" I meant "not clocks that are not module
clocks". Having a reset controller function in there is fine.

So it seems you do have a clock provider that provides module clocks,
and can mark them CLK_RUNTIME_PM.

>> On shmobile SoCs, all module clocks are controlled using the MSTP
>> (Module SToP) clocks.
>>
>> In my old RFC series "[PATCH/RFC 0/4] of: Register clocks for Runtime PM
>> with PM core" (https://lkml.org/lkml/2014/4/24/1118) the MSTP clock driver
>> advertised using a new CLK_RUNTIME_PM flag that its clocks are module
>> clocks and thus suitable for runtime PM.
>>
>> There were some issues with that series, but the general idea of letting a
>> clock driver advertise that all its clocks are module clocks could still be
>> useful. Then the power domain driver knows which clocks to manage.
>
> That sounds interesting. Although it would still mean that we need a way
> to associate a clock with the correct power domain. I guess the driver
> could do that by iterating over all available clocks in the device's
> clocks property and grab only those that are marked CLK_RUNTIME_PM.

Yes, that's the idea.

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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