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

[Doug Anderson]

Hi,

On Tue, Dec 5, 2023 at 9:35 AM Doug Anderson <dianders at chromium.org> wrote:
>
> Hi,
>
> On Tue, Dec 5, 2023 at 5:40 AM Laurent Pinchart
> <laurent.pinchart at 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 at 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 at kernel.org>
> > > > > Signed-off-by: Douglas Anderson <dianders at 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 at glider.be>
> > > >
> > > > Reviewed-by: Laurent Pinchart <laurent.pinchart at 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.

FWIW, I've sent out a new version of the series that removes most
panel-specific enable/prepare tracking and also adjusts the TODO to
make it clear that these warnings are expected for panel-simple and
panel-edp [1]. For all other panels my series removes the extra
drm_panel_disable() and drm_panel_unprepare().

I noticed that ${SUBJECT} patch hasn't landed yet, but from grepping I
couldn't find it used with any panels that I was touching... In any
case, it seems like it would be nice if it could land...

I'm not sure the best way to deal with panel-simple / panel-edp. I'm a
little scared to just remove the disable/unprepare since they are used
across so many different DRM modeset drivers, but the annoying thing
is that the warning shows up only on DRM modeset drivers that have
been fixed and _not_ on ones that weren't fixed. :( To get a warning
at the right times we'd need something that runs _after_ driver
shutdown to check whether the DRM modeset driver forgot to call
drm_atomic_helper_shutdown()...

[1] https://lore.kernel.org/r/20240503213441.177109-1-dianders@chromium.org