linux-kernel - Re: [PATCH] drm/panel: Avoid warnings w/ panel-simple/panel-edp at shutdown

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Message-ID: <CAD=FV=UdsuEiyPK2K3sYdQm50WNukA5pxD=wUaEAVQStNnNA_A@mail.gmail.com>
Date: Mon, 15 Jul 2024 09:40:05 -0700
From: Doug Anderson <dianders@...omium.org>
To: dri-devel@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Maxime Ripard <mripard@...nel.org>
Cc: Linus Walleij <linus.walleij@...aro.org>, Chris Morgan <macromorgan@...mail.com>, 
	Yuran Pereira <yuran.pereira@...mail.com>, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, 
	David Airlie <airlied@...il.com>, Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Jonathan Corbet <corbet@....net>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panel: Avoid warnings w/ panel-simple/panel-edp at shutdown

Hi,

On Fri, Jun 21, 2024 at 1:46 PM Doug Anderson <dianders@...omium.org> wrote:
>
> Hi,
>
> On Fri, Jun 21, 2024 at 1:45 PM Douglas Anderson <dianders@...omium.org> wrote:
> >
> > At shutdown if you've got a _properly_ coded DRM modeset driver then
> > you'll get these two warnings at shutdown time:
> >
> >   Skipping disable of already disabled panel
> >   Skipping unprepare of already unprepared panel
> >
> > These warnings are ugly and sound concerning, but they're actually a
> > sign of a properly working system. That's not great.
> >
> > We're not ready to get rid of the calls to drm_panel_disable() and
> > drm_panel_unprepare() because we're not 100% convinced that all DRM
> > modeset drivers are properly calling drm_atomic_helper_shutdown() or
> > drm_helper_force_disable_all() at the right times. However, having the
> > warning show up for correctly working systems is bad.
> >
> > As a bit of a workaround, add some "if" tests to try to avoid the
> > warning on correctly working systems. Also add some comments and
> > update the TODO items in the hopes that future developers won't be too
> > confused by what's going on here.
> >
> > Suggested-by: Daniel Vetter <daniel@...ll.ch>
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > ---
> > This patch came out of discussion on dri-devel on 2024-06-21
> > [1]. NOTE: I have put all changes into one patch since it didn't seem
> > to add anything to break up the updating of the TODO or the comments
> > in the core into separate patches since the patch is all about one
> > topic and all code is expected to land in the same tree.
> >
> > Previous versions:
> > v0: https://lore.kernel.org/r/20240604172305.v3.24.Ieb287c2c3ee3f6d3b0d5f49b29f746b93621749c@changeid/
> > v1: https://lore.kernel.org/r/20240611074846.1.Ieb287c2c3ee3f6d3b0d5f49b29f746b93621749c@changeid
> >
> > [1] https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&date=2024-06-21
> >
> >  Documentation/gpu/todo.rst           | 35 +++++++++++++---------------
> >  drivers/gpu/drm/drm_panel.c          | 18 ++++++++++++++
> >  drivers/gpu/drm/panel/panel-edp.c    | 26 ++++++++++++++-------
> >  drivers/gpu/drm/panel/panel-simple.c | 26 ++++++++++++++-------
> >  4 files changed, 68 insertions(+), 37 deletions(-)
>
> Ugh! I realized right after I hit "send" that I forgot to mark this as
> V2 and give it version history. Sorry! :( Please consider this to be
> v2. It's basically totally different than v1 based on today's IRC
> discussion, which should be linked above.
>
> If I need to send a new version I will send it as v3.

Is anyone willing to give me a Reviewed-by and/or Acked by for this
patch? ...or does anything want me to make any changes? Given all the
discussion we had, it would be nice to get this landed before we
forget what we agreed upon. :-P

-Doug