linux-kernel - Re: [PATCH] drm: DON'T require each CRTC to have a unique primary plane

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Message-ID: <f_BApfXCctltkOAAKup7ZXRsq8N81SZgbxIEFbHWzeoKZCo8z169Bkk4DDwk9WmMNKXpyxaMQCxbWzwVMgfNav0ZYVf3s_6bXRO89LKD_AM=@emersion.fr>
Date:   Mon, 29 Mar 2021 15:36:27 +0000
From:   Simon Ser <contact@...rsion.fr>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Maxime Ripard <maxime@...no.tech>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, od@...c.me,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] drm: DON'T require each CRTC to have a unique primary plane

On Monday, March 29th, 2021 at 5:32 PM, Paul Cercueil <paul@...pouillou.net> wrote:

> Making the second plane an overlay would break the ABI, which is never
> something I'm happy to do; but I'd prefer to do it now than later.

Yeah, I wonder if some user-space depends on this behavior somehow?

> I still have concerns about the user-space being "clever" enough to
> know it can disable the primary plane. Can e.g. wlroots handle that?

wlroots will always pick the first primary plane, and will never use
overlays. The plan is to use libliftoff [1] to make use of overlay
planes. libliftoff should already support the scenario you describe.

I think Weston supports that too.

[1]: https://github.com/emersion/libliftoff