Message-ID: <CAMuHMdU7W+f3nZ_ckHOFsmmK6V9HzK0-fNtcu8kgjTSeU89AqQ@mail.gmail.com>
Date: Wed, 13 Aug 2025 13:58:40 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Saravana Kannan <saravanak@...gle.com>, Stephen Boyd <sboyd@...nel.org>, linux-pm@...r.kernel.org, 
	"Rafael J . Wysocki" <rafael@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Michael Grzeschik <m.grzeschik@...gutronix.de>, 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>, Hiago De Franco <hiago.franco@...adex.com>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v3 00/24] pmdomain: Add generic ->sync_state() support to genpd

Hi Ulf,

On Tue, 12 Aug 2025 at 12:01, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> On Thu, 7 Aug 2025 at 11:38, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Wed, 30 Jul 2025 at 12:29, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > > On Wed, 30 Jul 2025 at 11:56, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > > On Wed, 9 Jul 2025 at 13:31, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > > > > On Tue, 1 Jul 2025 at 13:47, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > > > > > Changes in v3:
> > > > > >         - Added a couple of patches to adress problems on some Renesas
> > > > > >         platforms. Thanks Geert and Tomi for helping out!
> > > > > >         - Adressed a few comments from Saravanna and Konrad.
> > > > > >         - Added some tested-by tags.
> > > > >
> > > > > I decided it was time to give this a try, so I have queued this up for
> > > > > v6.17 via the next branch at my pmdomain tree.
> > > > >
> > > > > If you encounter any issues, please let me know so I can help to fix them.
> > > >
> > > > Thanks for your series!  Due to holidays, I only managed to test
> > > > this very recently.
> > > >
> > > > Unfortunately I have an issue with unused PM Domains no longer being
> > > > disabled on R-Car:
> > > >   - On R-Car Gen1/2/3, using rcar-sysc.c, unused PM Domains are never
> > > >     disabled.
> > > >   - On R-Car Gen4, using rcar-gen4-sysc.c, unused PM Domains are
> > > >     sometimes not disabled.
> > > >     At first, I noticed the IOMMU driver was not enabled in my config,
> > > >     and enabling it did fix the issue.  However, after that I still
> > > >     encountered the issue in a different config that does have the
> > > >     IOMMU driver enabled...
> > > >
> > > > FTR, unused PM Domains are still disabled correctly on R/SH-Mobile
> > > > (using rmobile-sysc.c) and on BeagleBone Black. Note that these use
> > > > of_genpd_add_provider_simple(), while all R-Car drivers use
> > > > of_genpd_add_provider_onecell().  Perhaps there is an issue with
> > > > the latter?  If you don't have a clue, I plan to do some more
> > > > investigation later...
> >
> > of_genpd_add_provider_onecell() has:
> >
> >     if (!dev)
> >             sync_state = true;
> >     else
> >             dev_set_drv_sync_state(dev, genpd_sync_state);
> >
> >     for (i = 0; i < data->num_domains; i++) {
> >             ...
> >             if (sync_state && !genpd_is_no_sync_state(genpd)) {
> >                     genpd->sync_state = GENPD_SYNC_STATE_ONECELL;
> >                     device_set_node(&genpd->dev, fwnode);
> >                     sync_state = false;
> >                     ^^^^^^^^^^^^^^^^^^^
> >             }
> >             ...
> >     }
> >
> > As the R-Car SYSC drivers are not platform drivers, dev is NULL, and
> > genpd->sync_state is set to GENPD_SYNC_STATE_ONECELL for the first PM
> > Domain only.  All other domains have the default value of sync_state
> > (0 = GENPD_SYNC_STATE_OFF).  Hence when genpd_provider_sync_state()
> > is called later, it ignores all but the first domain.
> > Apparently this is intentional, as of_genpd_sync_state() tries to
> > power off all domains handled by the same controller anyway (see below)?
>
> Right, this is intentional and mainly because of how fw_devlink works.
>
> fw_devlink is limited to use only the first device - if multiple
> devices share the same fwnode. In principle, we could have picked any
> of the devices in the array of genpds here - and reached the same
> result.

OK, just like I already assumed...

> > > > BTW, the "pending due to"-messages look weird to me.
> > > > On R-Car M2-W (r8a7791.dtsi) I see e.g.:
> > > >
> > > >     genpd_provider ca15-cpu0: sync_state() pending due to e6020000.watchdog
> > > >     renesas-cpg-mssr e6150000.clock-controller: sync_state() pending
> > > > due to e6020000.watchdog
> > > >
> > > > ca15-cpu0 is the PM Domain holding the first CPU core, while
> > > > the watchdog resides in the always-on Clock Domain, and uses the
> > > > clock-controller for PM_CLK handling.
> >
> > Unfortunately the first PM Domain is "ca15-cpu0", which is blocked on
> > these bogus pending states, and no PM Domain is powered off.
>
> I see, thanks for the details. I am looking closer at this.
>
> In any case, this is the main issue, as it prevents the ->sync_state()
> callback to be called. Hence the "genpd->stay_on" will also *not* be
> cleared for any of the genpd's for the genpd-provider.

I was under the impression there is a time-out, after which the
.sync_state() callback would be called anyway, just like for probe
deferral due to missing optional providers like DMACs and IOMMUs.
Apparently that is not the case?

> > If I remove the "sync_state = false" above, genpd_provider_sync_state()
> > considers all domains, and does power down all unused domains (even
> > multiple times, as expected).
>
> I think those are getting called because with the change above, there
> is no device_link being tracked. As stated above, fw_devlink is
> limited to use only one device - if multiple devices share the same
> fwnode.

Indeed.

> In other words, the ->sync_state() callbacks are called even if the
> corresponding consumer devices have not been probed yet.

Hence shouldn't there be a timeout, as the kernel may not even have
a driver for one or more consumer devices?

> > Upon closer look, all "pending due to" messages I see claim that the
> > first (index 0) PM Domain is pending on some devices, while all of
> > these devices are part of a different domain (usually the always-on
> > domain, which is always the last (32 or 64) on R-Car).
> >
> > So I think there are two issues:
> >   1. Devices are not attributed to the correct PM Domain using
> >      fw_devlink sync_state,
> >   2. One PM Domain of a multi-domain controller being blocked should
> >      not block all other domains handled by the same controller.
>
> Right, that's a current limitation with fw_devlink. To cope with this,
> it's possible to enforce the ->sync_state() callback to be invoked
> from user-space (timeout or explicitly) for a device.
>
> Another option would be to allow an opt-out behavior for some genpd's
> that are powered-on at initialization. Something along the lines of
> the below.
>
> From: Ulf Hansson <ulf.hansson@...aro.org>
> Date: Tue, 29 Jul 2025 14:27:22 +0200
> Subject: [PATCH] pmdomain: core: Allow powered-on PM domains to be powered-off
>  during boot

[...]

I gave this a try (i.e. "| GENPD_FLAG_NO_STAY_ON" in rcar-sysc.c), but
this doesn't make any difference.  I assume this would only work when
actively calling genpd_power_off() (i.e. not from of_genpd_sync_state()
or genpd_provider_sync_state())?

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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