linux-kernel - Re: [RFC PATCH 10/10] drm/panel: Update TODO list item for cleaning up prepared/enabled tracking

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Date:   Mon, 7 Aug 2023 08:41:35 +0200
From:   Maxime Ripard <mripard@...nel.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     dri-devel@...ts.freedesktop.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.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: [RFC PATCH 10/10] drm/panel: Update TODO list item for cleaning
 up prepared/enabled tracking

On Fri, Aug 04, 2023 at 02:06:13PM -0700, Douglas Anderson wrote:
> Now that most panels have been updated not to track/double-check their
> prepared/enabled state update the TODO with next steps.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
>  Documentation/gpu/todo.rst | 33 +++++++++++++--------------------
>  1 file changed, 13 insertions(+), 20 deletions(-)
> 
> diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
> index 139980487ccf..c73d9dbebbf4 100644
> --- a/Documentation/gpu/todo.rst
> +++ b/Documentation/gpu/todo.rst
> @@ -460,26 +460,19 @@ Contact: Thomas Zimmermann <tzimmermann@...e.de>
>  
>  Level: Starter
>  
> -Clean up checks for already prepared/enabled in panels
> -------------------------------------------------------
> -
> -In a whole pile of panel drivers, we have code to make the
> -prepare/unprepare/enable/disable callbacks behave as no-ops if they've already
> -been called. To get some idea of the duplicated code, try::
> -
> -  git grep 'if.*>prepared' -- drivers/gpu/drm/panel
> -  git grep 'if.*>enabled' -- drivers/gpu/drm/panel
> -
> -In the patch ("drm/panel: Check for already prepared/enabled in drm_panel")
> -we've moved this check to the core. Now we can most definitely remove the
> -check from the individual panels and save a pile of code.
> -
> -In adition to removing the check from the individual panels, it is believed
> -that even the core shouldn't need this check and that should be considered
> -an error if other code ever relies on this check. The check in the core
> -currently prints a warning whenever something is relying on this check with
> -dev_warn(). After a little while, we likely want to promote this to a
> -WARN(1) to help encourage folks not to rely on this behavior.
> +Never double prepare/enable/disable/unprepare a panel
> +-----------------------------------------------------
> +
> +As of commit d2aacaf07395 ("drm/panel: Check for already prepared/enabled in
> +drm_panel"), we have a check in the drm_panel core to make sure nobody
> +double-calls prepare/enable/disable/unprepare. However, that extra double-check
> +shouldn't be necessary. The caller should always be matching up calls of
> +prepare/unprepare and matching up calls of enable/disable.
> +
> +Hopefully the warning printed will encourage everyone to fix this. Eventually
> +we'll likely want to change this to a WARN_ON and (perhaps) fully remove the
> +check. NOTE: even if we remove the double-check, drm_panel core still needs
> +to track the enabled/prepared state for its own purposes.

Detailing what those purposes are would be nice :)

Maxime

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