Re: [PATCH] clk: rockchip: Set "ignore unused" for PMU M0 clocks on rk3399

[Javier Martinez Canillas]

Hello Heiko and Doug,

On Wed, Feb 15, 2017 at 2:01 PM, Heiko StÃbner <heiko@xxxxxxxxx> wrote:
> Am Mittwoch, 15. Februar 2017, 12:27:59 CET schrieb Javier Martinez Canillas:
>> Hello Doug,
>>
>> On Tue, Feb 14, 2017 at 6:01 PM, Douglas Anderson <dianders@xxxxxxxxxxxx>
> wrote:
>> > The PMU Cortex M0 on rk3399 is intended to be used for things like
>> > DDRFreq transitions, suspend/resume, and other things that are the
>> > purview of ARM Trusted Firmware and not the kernel.  As such, the
>> > kernel shouldn't be messing with the clocks.  Add CLK_IGNORE_UNUSED to
>> > these clocks.
>>
>> Isn't CLK_IS_CRITICAL a more suitable flag for this case?
>
> From the patch description it looks like the clock is expected to be
> controlled from firmware in most cases as I guess the Cortex M0 will be used
> for that all the time now. And the clock is not expected to run all the time.
>
> So I'd think clk_ignore_unused is the correct one. The whole clock-subtree for
> these clocks also does not get affected by other clocks, as it is
> independendly coming from PLLs.
>
>

I see. Thanks a lot for your explanations. I just asked because
CLK_IGNORE_UNUSED only prevents the clock to be disabled by
clk_disable_unused() but still can be disabled if a driver explicitly
looks it up and calls clk_disable() or if the clock is affected by
other clocks.

But I understand now that both scenarios are not possible. So yes,
CLK_IGNORE_UNUSED is more suitable in this case.

> Heiko

Best regards,
Javier