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

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Message-ID: <CACRpkdaT=zjrKtqS7h4Fq1sLOJ1MoxW9K-wMfWqOmD68owj+Kg@mail.gmail.com>
Date: Tue, 16 Jul 2024 22:19:10 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Douglas Anderson <dianders@...omium.org>
Cc: dri-devel@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Maxime Ripard <mripard@...nel.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

On Fri, Jun 21, 2024 at 10:45 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>

Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

This is the right thing to do.

Yours,
Linus Walleij