linux-kernel - Re: [PATCH] drm/imagination: Convert to dev_pm_domain_{at,de}tach

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Message-ID: <CAMuHMdWMh_oJFg-KtapcTDGvYWZ-hg_ZEJ2=E5Tp1apOEc8tnQ@mail.gmail.com>
Date: Fri, 23 Jan 2026 14:50:31 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Matt Coster <Matt.Coster@...tec.com>
Cc: Frank Binns <Frank.Binns@...tec.com>, Brajesh Gupta <Brajesh.Gupta@...tec.com>, 
	Alessio Belle <Alessio.Belle@...tec.com>, Alexandru Dadu <Alexandru.Dadu@...tec.com>, 
	Marek Vasut <marek.vasut@...lbox.org>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, 
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/imagination: Convert to dev_pm_domain_{at,de}tach_list()

Hi Matt,

On Fri, 23 Jan 2026 at 14:36, Matt Coster <Matt.Coster@...tec.com> wrote:
> On 22/01/2026 16:08, Geert Uytterhoeven wrote:
> > Call the dev_pm_domain_attach_list() and dev_pm_domain_detach_list()
> > helpers instead of open-coding multi PM Domain handling.
> >
> > This changes behavior slightly:
> >   - The new handling is also applied in case of a single PM Domain,
> >   - PM Domains are now referred to by index instead of by name, but
> >     "make dtbs_check" enforces the actual naming and ordering anyway,
> >   - There are no longer device links created between virtual domain
> >     devices, only between virtual devices and the parent device.
>
> We still need this guarantee, both at start and end of day. In the
> current implementation dev_pm_domain_attach_list() iterates forwards,
> but so does dev_pm_domain_detach_list(). Even if we changed that, I'd
> prefer not to rely on the implementation details when we can declare the
> dependencies explicitly.

Note that on R-Car, the PM Domains are nested (see e.g. r8a7795_areas[]),
so they are always (un)powered in the correct order.  But that may not
be the case in the integration on other SoCs.

> We had/have a patch (attached) kicking around internally to use the
> *_list() functions but keep the inter-domain links in place; it got held
> up by discussions as to whether we actually need those dependencies for
> the hardware to behave correctly. Your patch spurred me to run around
> the office and nag people a bit, and it seems we really do need to care
> about the ordering.

OK.

> Can you add the links back in for a V2 or I can properly send the
> attached patch instead, I don't mind either way.

Please move forward with your patch, you are the expert.
I prefer not to be blamed for any breakage ;-)

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