Re: [PATCH 1/2] PM / Domains: Add GENPD_FLAG_SUSPEND_ON flag

[Sibi Sankar]

On 2020-08-18 14:01, Ulf Hansson wrote:
> On Mon, 17 Aug 2020 at 18:49, Sibi Sankar <sibis@xxxxxxxxxxxxxx> wrote:
> > On 2020-08-17 14:14, Ulf Hansson wrote:
> > > On Thu, 13 Aug 2020 at 19:26, Sibi Sankar <sibis@xxxxxxxxxxxxxx> wrote:
> > >>
> > >> On 2020-08-13 18:04, Ulf Hansson wrote:
> > >> > On Wed, 12 Aug 2020 at 19:03, Sibi Sankar <sibis@xxxxxxxxxxxxxx> wrote:
> > >> >>
> > >> >> Uffe,
> > >> >> Thanks for taking time to review the
> > >> >> series!
> > >> >>
> > >> >> On 2020-08-12 15:15, Ulf Hansson wrote:
> > >> >> > On Tue, 11 Aug 2020 at 21:03, Sibi Sankar <sibis@xxxxxxxxxxxxxx> wrote:
> > >> >> >>
> > >> >> >> This is for power domains which needs to stay powered on for suspend
> > >> >> >> but can be powered on/off as part of runtime PM. This flag is aimed at
> > >> >> >> power domains coupled to remote processors which enter suspend states
> > >> >> >> independent to that of the application processor. Such power domains
> > >> >> >> are turned off only on remote processor crash/shutdown.
> > >> >> >
> > >> >> > As Kevin also requested, please elaborate more on the use case.
> > >> >> >
> > >> >> > Why exactly must the PM domain stay powered on during system suspend?
> > >> >> > Is there a wakeup configured that needs to be managed - or is there a
> > >> >> > co-processor/FW behaviour that needs to be obeyed to?
> > >> >>
> > >> >> Yes this is a co-processor behavior that
> > >> >> needs to be obeyed. Specifically application
> > >> >> processor notifies the Always on Subsystem
> > >> >> (AOSS) that a particular co-processor is up
> > >> >> using the power domains exposed by AOSS QMP
> > >> >> driver. AOSS uses this information to wait
> > >> >> for the co-processors to suspend before
> > >> >> starting its sleep sequence. The application
> > >> >> processor powers off these power domains only
> > >> >> if the co-processor has crashed or powered
> > >> >> off.
> > >> >
> > >> > Thanks for clarifying!
> > >> >
> > >> > Although, can you please elaborate a bit more on the actual use case?
> > >> > What are the typical co-processor and what drivers are involved in
> > >> > managing it?
> > >>
> > >> The co-processors using the power domains
> > >> exposed by qcom_aoss driver are modem,
> > >> audio dsp, compute dsp managed using
> > >> qcom_q6v5_mss and qcom_q6v5_pas driver.
> > >>
> > >> >
> > >> > As you may know, runtime PM becomes disabled during system suspend of
> > >> > a device. Which means, if the driver tries to power off the
> > >> > coprocessor (via calling pm_runtime_put() for example), somewhere in
> > >> > the system suspend phase of the corresponding device, its attached PM
> > >> > domain stays powered on when managed by genpd.
> > >>
> > >> The drivers aren't really expected
> > >> do anything during suspend/resume
> > >> pretty much because the co-processors
> > >> enter low-power modes independent to
> > >> that of the application processor. On
> > >> co-processor crash the remoteproc core
> > >> does a pm_stay_awake followed by a
> > >> pm_relax after crash recovery.
> > >
> > > Okay, thanks again for clarifying. You have convinced me about the
> > > need for a new flag to cope with these use cases.
> > >
> > > Would you mind updating the commit message with some of the
> > > information you just provided?
> > >
> > > Additionally, to make it clear that the flag should be used to keep
> > > the PM domain powered on during system suspend, but only if it's
> > > already powered on - please rename the flag to GENPD_FLAG_NO_SUSPEND,
> > > and update the corresponding description of it in the header file.
> >
> > Thanks, naming it ^^ makes more sense :)
> >
> > https://lore.kernel.org/lkml/340a7aafcf0301ff3158a4e211992041@xxxxxxxxxxxxxx/
> >
> > Also we wouldn't want to power on
> > runtime suspended power domains with
> > the NO_SUSPEND flag set, on resume as
> > explained ^^. Do you agree with that
> > as well?
>
> Actually no.
>
> Instead, I think that deserves a separate flag, as it may very well
> turn out that resuming can be skipped for other cases than
> "NO_SUSPEND".
>
> Therefore, please add a GENPD_FLAG_NO_RESUME for this.

Thanks I'll do that in v2

> Kind regards
> Uffe

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