Re: [PATCH 15/18] drivers: firmware: psci: Support CPU hotplug for the hierarchical model

From: Ulf Hansson
Date: Mon Jun 10 2019 - 06:26:46 EST

On Fri, 7 Jun 2019 at 17:31, Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
> On Mon, May 13, 2019 at 09:22:57PM +0200, Ulf Hansson wrote:
> > When the hierarchical CPU topology is used and when a CPU has been put
> > offline (hotplug), that same CPU prevents its PM domain and thus also
> > potential master PM domains, from being powered off. This is because genpd
> > observes the CPU's attached device as being active from a runtime PM point
> > of view.
> >
> > To deal with this, let's decrease the runtime PM usage count by calling
> > pm_runtime_put_sync_suspend() of the attached struct device when putting
> > the CPU offline. Consequentially, we must then increase the runtime PM
> > usage count, while putting the CPU online again.
> >
> Why is this firmware/driver specific ? Why can't this be dealt in core
> pm-domain ? I am concerned that if any other architectures or firmware
> method decides to use this feature, this need to be duplicated there.

What is the core pm-domain? Do you refer to the generic PM domain (genpd), no?

In such case, this is not the job of genpd, but rather the opposite
(to *monitor* the reference count).

> The way I see this is pure reference counting and is hardware/firmware/
> driver agnostic and can be made generic.

As stated in the another reply, I would rather start with having more
things driver specific rather than generic. Later on we can always
consider to move/split things, when there are more users.

In this particular case, the runtime PM reference counting is done on
the struct device*, that genpd returned via
dev_pm_domain_attach_by_name(). And because
dev_pm_domain_attach_by_name() is called from PSCI code, I decided to
keep this struct device* internal to PSCI.

Kind regards