Re: [PATCH v2] PM: domains: Prevent power off for parent unless child is in deepest state

[Ulf Hansson]

On Tue, 15 Feb 2022 at 22:49, Dmitry Osipenko <digetx@xxxxxxxxx> wrote:
>
> 04.02.2022 13:16, Ulf Hansson пишет:
> > A PM domain managed by genpd may support multiple idlestates. During
> > genpd_power_off() a genpd governor may be asked to select one of the
> > idlestates based upon the dev PM QoS constraints, for example.
> >
> > However, there is a problem with the behaviour around this in genpd. More
> > precisely, a parent-domain is allowed to be powered off, no matter of what
> > idlestate that has been selected for the child-domain.
> >
> > So far, we have not received any reports about errors from the current
> > behaviour. However, there is an STMicro platform that is being worked on,
> > which can't cope with this.
>
> Could you please provide some technical info about why STMicro platform
> can't cope with that?

There is a parent domain with one power-off state. The parent domain
has a few devices attached to it, which means they need to be managed
to together. The parent domain is controlling a shared power rail.

The child domain, which has multiple idle states to choose from, also
has some devices attached to it. The child domain is controlling a
system clock, but also relies on the shared power rail that is managed
by the parent domain.

Obviously, these idle states are managed by firmware.

I hope that made it a bit more clear?

Kind regards
Uffe