Re: [PATCH] drm: renesas: shmobile: Call drm_helper_force_disable_all() at shutdown time

From: Doug Anderson <dianders@chromium.org>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	 David Airlie <airlied@gmail.com>,
	Daniel Vetter <daniel@ffwll.ch>,
	Maxime Ripard <mripard@kernel.org>,
	 dri-devel@lists.freedesktop.org,
	linux-renesas-soc@vger.kernel.org
Subject: Re: [PATCH] drm: renesas: shmobile: Call drm_helper_force_disable_all() at shutdown time
Date: Tue, 5 Dec 2023 09:35:12 -0800	[thread overview]
Message-ID: <CAD=FV=WFykYh2PAw5G3uL-64LG45O3cPRiwN1HOfMAoeLK5KMg@mail.gmail.com> (raw)
In-Reply-To: <20231205134050.GG17394@pendragon.ideasonboard.com>

Hi,

On Tue, Dec 5, 2023 at 5:40 AM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> On Tue, Dec 05, 2023 at 02:31:24PM +0100, Geert Uytterhoeven wrote:
> > On Tue, Dec 5, 2023 at 1:16 PM Laurent Pinchart wrote:
> > > On Tue, Dec 05, 2023 at 12:30:02PM +0100, Geert Uytterhoeven wrote:
> > > > From: Douglas Anderson <dianders@chromium.org>
> > > >
> > > > Based on grepping through the source code, this driver appears to be
> > > > missing a call to drm_atomic_helper_shutdown() at system shutdown time.
> > > > This is important because drm_helper_force_disable_all() will cause
> > > > panels to get disabled cleanly which may be important for their power
> > > > sequencing.  Future changes will remove any custom powering off in
> > > > individual panel drivers so the DRM drivers need to start getting this
> > > > right.
> > > >
> > > > The fact that we should call drm_atomic_helper_shutdown() in the case of
> > > > OS shutdown comes straight out of the kernel doc "driver instance
> > > > overview" in drm_drv.c.
> > > >
> > > > Suggested-by: Maxime Ripard <mripard@kernel.org>
> > > > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > > > Link: https://lore.kernel.org/r/20230901164111.RFT.15.Iaf638a1d4c8b3c307a6192efabb4cbb06b195f15@changeid
> > > > [geert: s/drm_helper_force_disable_all/drm_atomic_helper_shutdown/]
> > > > [geert: shmob_drm_remove() already calls drm_atomic_helper_shutdown]
> > > > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> > >
> > > Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> >
> > Thanks!
> >
> > > > Panel-simple does print two new warnings:
> > > >
> > > >     +panel-simple panel: Skipping disable of already disabled panel
> > > >     +panel-simple panel: Skipping unprepare of already unprepared panel
> > >
> > > Have you investigated where this comes from ?
> >
> > Meh, I knew I forgot something ;-)
> >
> > The panel is unprepared and disabled a first time from shmob_drm's
> > .shutdown() callback:
> >
> >   shmob_drm_shutdown
> >     drm_atomic_helper_shutdown
> >       drm_atomic_helper_disable_all
> >         drm_atomic_commit
> >           drm_atomic_helper_commit
> >             commit_tail
> >               drm_atomic_helper_commit_tail
> >                 drm_atomic_helper_commit_modeset_disables
> >                   disable_outputs
> >                     drm_atomic_bridge_chain_disable
> >                         drm_panel_disable
> >                     drm_atomic_bridge_chain_post_disable
> >                         drm_panel_unprepare
> >
> > And a second time from simple_panel's .shutdown() callback():
> >
> >   panel_simple_platform_shutdown
> >     panel_simple_shutdown
> >       drm_panel_disable
> >       drm_panel_unprepare
>
> That looks like what Doug mentioned should be removed in the commit
> message of this patch (a confirmation would be nice). It should be fine
> for now.

Yup, this is completely expected right now and is actually a _good_
sign that your patch is doing what it should be. We unfortunately
can't remove the panel_simple_shutdown() until all DRM modeset drivers
(or at least all the ones that could be used w/ panel_simple) are
properly calling drm_helper_force_disable_all(), though.

-Doug