Re: [PATCH v3 1/2] soc/tegra: pmc: Query PCLK clock rate at probe time

[Dmitry Osipenko]

02.08.2019 16:38, Peter De Schrijver ÐÐÑÐÑ:
> On Tue, Jul 30, 2019 at 08:40:19PM +0300, Dmitry Osipenko wrote:
>> The PCLK clock is running off SCLK, which is a critical clock that is
>> very unlikely to randomly change its rate. It is possible to get a
>> lockup if kernel decides to enter LP2 cpuidle from a clk-notifier, which
>> happens occasionally in a case of Tegra30 EMC driver that waits for the
>> clk-change event in the clk-notify handler, because CCF's 'prepare' mutex
>> in kept locked and thus clk_get_rate() wants to sleep with interrupts
>> being disabled.
>>
> 
> I don't think this is the right solution. Eventually we will want to
> scale sclk and pclk because the clock tree power of those is not
> insignificant. Maybe register a notifier which updates the PMC timer
> values when pclk changes?

I also had a thought about the notifier for pclk, but wasn't sure if
it's really worthwhile right now since there is no real use-case and
it's not obvious when such case will materialize. So, I'd say that
solution is correct but incomplete.

I'll make a v4 with the notifier, since you're asking about it. Thanks
for the review!