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

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Date:   Tue, 13 Sep 2022 11:08:04 -0400
From:   Harry Wentland <harry.wentland@....com>
To:     Javier Martinez Canillas <javierm@...hat.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 2022-09-13 10:46, Javier Martinez Canillas wrote:
> 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 ?
> 

After re-reading I see what you mean.

A sentence to the effect of "Some drivers require the primary plane
to be a fullscreen scanout buffer..." or similar might help clarify
that this isn't universal but helpful for drivers who require this
constraint.

Harry

>> Harry
>>
>