linux-kernel - Re: [PATCH 3/5] pmdomain: renesas: rcar-sysc: Don't keep unused PM domains powered-on

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Message-ID: <CAPDyKFrZ4hA0O3PRUJwwetQYsgAt50tPo_hL90epUx1T8kFDEQ@mail.gmail.com>
Date: Thu, 11 Sep 2025 12:31:47 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>, 
	Saravana Kannan <saravanak@...gle.com>, linux-pm@...r.kernel.org, 
	Stephen Boyd <sboyd@...nel.org>, "Rafael J . Wysocki" <rafael@...nel.org>, Heiko Stuebner <heiko@...ech.de>, 
	Sebastian Reichel <sebastian.reichel@...labora.com>, Sebin Francis <sebin.francis@...com>, 
	Diederik de Haas <didi.debian@...ow.org>, Bjorn Andersson <andersson@...nel.org>, 
	Abel Vesa <abel.vesa@...aro.org>, Peng Fan <peng.fan@....nxp.com>, 
	Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, Johan Hovold <johan@...nel.org>, 
	Maulik Shah <maulik.shah@....qualcomm.com>, Michal Simek <michal.simek@....com>, 
	Konrad Dybcio <konradybcio@...nel.org>, Thierry Reding <thierry.reding@...il.com>, 
	Jonathan Hunter <jonathanh@...dia.com>, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] pmdomain: renesas: rcar-sysc: Don't keep unused PM
 domains powered-on

On Thu, 11 Sept 2025 at 11:02, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Ulf,
>
> On Tue, 9 Sept 2025 at 13:11, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > The recent changes to genpd makes a genpd OF provider that is powered-on at
> > initialization to stay powered-on, until the ->sync_state() callback is
> > invoked for it.
> >
> > This may not happen at all, if we wait for a consumer device to be probed,
> > leading to wasting energy. There are ways to enforce the ->sync_state()
> > callback to be invoked, through sysfs or via the probe-defer-timeout, but
> > none of them in its current form are a good fit for rcar-sysc PM domains.
> >
> > Let's therefore opt-out from this behaviour of genpd for now, by using the
> > GENPD_FLAG_NO_STAY_ON.
> >
> > Link: https://lore.kernel.org/all/20250701114733.636510-1-ulf.hansson@linaro.org/
> > Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> > Fixes: 0e789b491ba0 ("pmdomain: core: Leave powered-on genpds on until sync_state")
> > Fixes: 13a4b7fb6260 ("pmdomain: core: Leave powered-on genpds on until late_initcall_sync")
> > Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
>
> > --- a/drivers/pmdomain/renesas/rcar-sysc.c
> > +++ b/drivers/pmdomain/renesas/rcar-sysc.c
> > @@ -241,6 +241,7 @@ static int __init rcar_sysc_pd_setup(struct rcar_sysc_pd *pd)
> >                 }
> >         }
> >
> > +       genpd->flags |= GENPD_FLAG_NO_STAY_ON;
>
> So this applies to all PM Domains.  While this doesn't hurt, perhaps it
> should not be set for always-on domains, and thus moved up, to become
> an "else" branch in the "if/else if/..."-logic handling always-on
> domains at the top of the function?
>
> This applies to rar-gen4-sysc.c, too.

You have a point, but currently this doesn't really matter. Genpd will
not power-off always-on-domains no matter whether
GENPD_FLAG_NO_STAY_ON is set or not.

The whole purpose from my side was to restore the behaviour we had
before, for the Reneas PM domains. I tend to think that it's better to
apply the $subject patch as is - and leave improvements to be made on
top.

Thanks a lot for testing and reviewing!

[...]

Kind regards
Uffe