Re: [PATCH 3/3] PM: domains: Add a ->dev_get_performance_state() callback to genpd

07.09.2021 12:57, Ulf Hansson пишет:

I don't mind extending the genpd API, but it needs to serve a good purpose.

As I said earlier, genpd doesn't know nor can control how the consumer
driver deploys runtime PM. Unfortunately, that also includes genpd
providers, as the behavior isn't a platform or PM domain specific
thing. This means genpd needs to be generic enough so it works for all
cases.

In the $subject patch, we rely on the pm_runtime_suspended() check in
dev_pm_genpd_set_performance_state(), which should work for all cases,
even if it may be sub-optimal for some scenarios.

Note that, in the approach your suggested [1],
pm_runtime_status_suspended() is used instead. This doesn't work when
a consumer driver doesn't enable runtime PM - or calls
pm_runtime_set_active() during ->probe(), because
genpd_runtime_resume() won't be invoked to restore the gpd->rpm_state.

That said, I wouldn't mind to simply skip adding the
->dev_get_performance_state() all together, if that is what you
prefer? In this way, it becomes the responsibility for the consumer
driver to do right thing, with the cost of some boilerplate code added
in its ->probe() routine.

Until a day ago, it wasn't clear to me that consumer drivers now can set
up rpm_pstate during probe(), which is a cleaner solution that works
well. So let's skip adding the questionable ->dev_get_performance_state().

The boilerplate code in the probe() is minimal in comparison to a
previous variant with the state-syncing done by rpm-resume callbacks of
consumer drivers, it's good enough.