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

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Date: Fri, 21 Jun 2024 13:46:53 -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 1:45 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.

-Doug