Re: [PATCH 1/2] soc: qcom: aoss: Don't wait for IRQ if we might be in suspend/resume noirq

[Doug Anderson]

Hi,

On Thu, Aug 6, 2020 at 10:33 AM Sibi Sankar <sibis@xxxxxxxxxxxxxx> wrote:
>
> On 2020-08-06 22:40, Doug Anderson wrote:
> > Hi,
> >
> > On Thu, Aug 6, 2020 at 7:36 AM Sibi Sankar <sibis@xxxxxxxxxxxxxx>
> > wrote:
> >>
> >> On 2020-08-06 04:32, Stephen Boyd wrote:
> >> > +Sibi who wrote the code
> >> >
> >> > Quoting Doug Anderson (2020-08-05 13:24:06)
> >> >>
> >> >> On Wed, Aug 5, 2020 at 10:36 AM Stephen Boyd <swboyd@xxxxxxxxxxxx>
> >> >> wrote:
> >> >> >
> >> >> > Why is the genpd being powered off at all? It looks like the driver is
> >> >> > written in a way that it doesn't expect this to happen. See where
> >> >> > adsp_pds_disable() is called from. Looks like the remoteproc "stop"
> >> >> > callback should be called or the driver should be detached.
> >> >> >
> >> >> > It sort of looks like the genpd is expected to be at the max level all
> >> >> > the time (it sets INT_MAX in adsp_pds_enable(), cool).
> >> >>
> >> >> In general in Linux there are some things that, at suspend time, get
> >> >> done behind a driver's back.  The regulator API, for instance, allows
> >> >> for regulators to be turned off in suspend even if a driver leaves
> >> >> them on.  Sure, it's good practice for a driver to be explicit but the
> >> >> regulator suspend states do allow for the more heavy-handed approach.
> >> >>
> >> >> I guess I assume that genpd is a bit similar.  If a driver leaves a
> >> >> genpd on all the time then it will still be turned off at suspend time
> >> >> and then turned back on at resume time.  It seems like it must be part
> >> >> of the genpd API.  Specifically genpd_sync_power_off() says: "Check if
> >> >> the given PM domain can be powered off (during system suspend or
> >> >> hibernation) and do that if so."  That makes it seem like it's how
> >> >> genpd works.
> >> >>
> >> >> Reading all the descriptions of things like GENPD_FLAG_ALWAYS_ON,
> >> >> GENPD_FLAG_ACTIVE_WAKEUP, GENPD_FLAG_RPM_ALWAYS_ON makes me even more
> >> >> convinced that it's normal (unless otherwise specified) for genpds to
> >> >> get turned off in suspend even if a driver just blindly left them on.
> >> >>
> >> >> Presumably if this "modem" genpd is supposed to stay on in suspend
> >> >> time it should have been marked "always on"?  I'd guess we'd need to
> >> >> add "GENPD_FLAG_ALWAYS_ON" in some (or all?) cases in qmp_pd_add() if
> >> >> this was true?
> >> >
> >> > Agreed. I can't read the mind of Sibi so I can only guess that Sibi
> >> > wasn't expecting this behavior by reading the driver structure. That
> >> > could be a wrong assumption.
> >> >
> >> >>
> >> >>
> >> >> > Maybe we need to
> >> >> > add some sort of suspend hooks to the remote proc driver instead? Where
> >> >> > those suspend hooks are called earlier and drop the genpd performance
> >> >> > state request but otherwise leave it enabled across suspend?
> >> >>
> >> >> I think you're saying:
> >> >>
> >> >> a) You think it's a bug today that the "modem" genpd is being powered
> >> >> off in suspend.  Any evidence to back this up?
> >> >>
> >> >> b) Assuming it's a bug today, we should mark the "modem" as
> >> >> GENPD_FLAG_ALWAYS_ON.
> >> >>
> >> >> c) If there are genpds that sometimes should be left on in suspend but
> >> >> sometimes not (and that doesn't match up with what
> >> >> GENPD_FLAG_ACTIVE_WAKEUP does), then we'd have to pass
> >> >> GENPD_FLAG_ALWAYS_ON as a flag and then add suspend hooks to make the
> >> >> decision for us.
> >>
> >> Doug/Stephen,
> >>
> >> Yes this is a bug, we wouldn't want
> >> to disable aoss_qmp genpd for modem
> >> during suspend (when the modem is
> >> running). The qmp send for modem
> >> is the primary means through which
> >> aoss determines whether to wait for
> >> modem before proceeding to sleep. So
> >> looks like updating the flag with
> >> GENPD_FLAG_ACTIVE_WAKEUP is the way
> >> to go. But introducing another flag
> >> that doesn't touch genpd's during
> >> suspend/resume should also work.
> >
> > OK, sounds good.  As per out-of-band conversation:
> >
> > * You'll plan to post a patch updating the flag.
> >
> > * There's still nothing here that says my patch is the wrong thing to
> > do also.  It seems like genpd poweroff routine are expected to be able
> > to run at "noirq" time so we should make sure we are able to do that.
> >
> > I'm also curious: my patch doesn't affect the behavior.  The genpd
> > would be powered off with or without my patch, my patch just removes a
> > pointless 1 second delay.  Therefore I guess today there is some type
> > of bug because the genpd is being turned off.  What would be the
> > visible impact of that bug?  ...or is it somehow masked by something
> > else keeping this power on so it wasn't an issue right now?
>
> I've been told AOSS decides to wait
> for modem suspend if its been notified
> that modem is on through qmp_send. AFAIK
> we never ran into this because AOSS sleep
> sequence starts after xo-shutdown which
> wont be reached in the presence of active
> rpmh votes from modem.
>
> Regardless we definitely want this genpd left
> untouched during suspend/resume.

With Sibi's patch [1] then ${SUBJECT} patch is no longer needed since
we are no longer called during "noirq" / "syscore" time.  Assuming
Sibi's patches (or something similar to them) are OK, we can consider
this patch abandoned.  I'll re-post patch #2 on its own once we get
confirmation that Sibi's patches are OK w/ folks.

[1] https://lore.kernel.org/r/20200811190252.10559-2-sibis@xxxxxxxxxxxxxx

-Doug