Date:   Thu, 6 Aug 2020 10:10:44 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Sibi Sankar <sibis@...eaurora.org>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Alex Elder <elder@...aro.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Andy Gross <agross@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] soc: qcom: aoss: Don't wait for IRQ if we might be in
 suspend/resume noirq

Hi,

On Thu, Aug 6, 2020 at 7:36 AM Sibi Sankar <sibis@...eaurora.org> 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@...omium.org>
> >> 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?

-Doug


-Doug

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