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

Geert Uytterhoeven
2014-05-01T14:46:35Z

Hi Grant,

On Thu, May 1, 2014 at 3:56 PM, Grant Likely <grant.likely@secretlab.ca> wrote:
> On Thu, May 1, 2014 at 2:41 PM, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>> On Thu, May 1, 2014 at 10:03 AM, Grant Likely <grant.likely@secretlab.ca> wrote:
>>> On Wed, 30 Apr 2014 23:54:37 +0200, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>>>> On Tue, Apr 29, 2014 at 3:16 PM, Grant Likely <grant.likely@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:
>> Set CLK_RUNTIME_PM flag".
>
> This is where I have issue. You're *assuming* clock drivers are
> initialized much earlier. That is not guaranteed. It is perfectly
> valid for clocks to be set up by a normal device driver, just like for
> interrupt controllers or gpio controllers.

OK, I didn't know that. In that case, nothing happens, and everything
works like before. So the drivers still have to take care of the
clocks themselves.

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