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

Grant Likely
2014-05-01T13:56:32Z

On Thu, May 1, 2014 at 2:41 PM, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> Hi Grant,
>
> 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.

g.