linux-kernel - Re: [PATCH v2] drm/plane-helper: Add a drm_plane_helper_atomic

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Date:   Tue, 13 Sep 2022 16:46:31 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Harry Wentland <harry.wentland@....com>,
        linux-kernel@...r.kernel.org
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2] drm/plane-helper: Add a
 drm_plane_helper_atomic_check() helper

On 9/13/22 15:49, Harry Wentland wrote:
> 
> 
> On 2022-09-13 05:33, Javier Martinez Canillas wrote:
>> Provides a default plane state check handler for primary planes that are a
>> fullscreen scanout buffer and whose state scale and position can't change.
>>
> 
> Even though this might be how some drivers are handling the primary
> plane this assumption is not universal. For example, on ChromeOS when
> the (default) underlay strategy is selected the compositor will
> position the video plane as the bottom-most plane and mark it
> as primary, while the desktop plane is marked as overlay and
> will contain an alpha cutout to show the underlying video.
>
> In this case the video plane (primary) won't span the screen
> and is regularly panned and resized.
>

I see. Interesting.

> No objections to this change as it helps share code between drivers,
> but maybe specify that this behavior is a unique requirement of
> these drivers.
> 

I tried to make it clear in the comment by mentioning that this helper
is applicable for drivers whose primary plane is always fullscreen and
can't scale or change position.

Any suggestions of what's missing in the helper kernel-doc comment to be
more clear ?

> Harry
> 

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat