[PATCH/RFC 3/4] of/clk: Register clocks suitable for Runtime PM with the PM core

Geert Uytterhoeven geert at linux-m68k.org
Thu May 1 06:41:11 PDT 2014

Hi Grant,

On Thu, May 1, 2014 at 10:03 AM, Grant Likely <grant.likely at secretlab.ca> wrote:
> On Wed, 30 Apr 2014 23:54:37 +0200, Geert Uytterhoeven <geert at linux-m68k.org> wrote:
>> On Tue, Apr 29, 2014 at 3:16 PM, Grant Likely <grant.likely at secretlab.ca> wrote:
>> > I also don't like that it tries to set up every clock, but there is no
>> > guarantee that the driver will even use it. I would rather see this
>> > behaviour linked into the function that obtains the clock at driver
>> > .probe() time. That way it can handle deferred probe correctly and it
>> > only sets up clocks that are actually used by the driver.
>> Not every clock. Only the clocks that are advertised by the clock driver as
>> being suitable for runtime_pm management. These are typically module
>> clocks, that must be enabled for the module to work. The driver doesn't
>> always want to handle these explicitly.
> Help me out here becasue I don't understand how that works with this
> patch set. From my, admittedly naive, reading it looks like the setup is
> being done at device creation time, but if the driver (or module) gets
> to declare which clocks need to be enabled in order to work, then that
> information is not available at device creation time.

Setup is indeed done at registration time. Note the check calling
clk_may_runtime_pm(), which is introduced in "[PATCH/RFC 1/4] clk: Add
CLK_RUNTIME_PM and clk_may_runtime_pm()".

Clock drivers are initialized much earlier, so they can set the CLK_RUNTIME_PM
flag for suitable clocks before platform devices are created from DT, cfr. the
example for shmobile MSTP clocks in "[PATCH/RFC 4/4] clk: shmobile: mstp:

I hope this makes it clear.



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

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