Re: [PATCH] PM/domains: add delayed power off capability

[Kevin Hilman <khilman@linaro.org>]

Peter De Schrijver <pdeschrijver@nvidia.com> writes:

>> > - If such a domain is going to be needed very soon in future, it makes
>> > sense to avoid its power down for at-least that much amount of time
>> > (which is what the proposed patch does).
>> 
>> ...and is also what the pluggable governors inside genpd are meant to
>> allow you to do.
>> 
>
> Unfortunately this is rather akward to implement in a genpd governor. The
> governor only gets called when the genpd core wants to power off a domain.
> It can then say yes or no. You could start a timer and on expiry call into
> genpd and use a flag to indicate to the governor (which will be called
> again), it should now allow the power off.
>
>> More specifically, what you said above: "if such a domain is going to be
>> needed very soon in the future" is just another way of saying it there
>> is a wakeup latency constraint.   Wakeup latency constratints are
>> handled by per-device PM QoS, which can be queried by a governor
>> associated with a genpd.
>
> No. This is not a wakeup latency constraint but rather an energy breakeven
> point constraint.

OK, that makes more sense, but the way it was described in the
changelog, it sounded like a wakeup latency constraint.

Speaking of the changelog, I would suggest it be updated to describe why
the other methods proposed here would not work.

Kevin