Re: [PATCH v2] drm/plane-helper: Add a drm_plane_helper_atomic_check() helper

From: Harry Wentland
Date: Tue Sep 13 2022 - 12:17:04 EST

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


>> Harry