linux-kernel - Re: [PATCH v6 6/6] drm/doc: Define KMS atomic state set

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Message-ID: <1b23576d-1649-ff5c-6273-b54729ea46d8@mailbox.org>
Date:   Thu, 17 Aug 2023 12:37:49 +0200
From:   Michel Dänzer <michel.daenzer@...lbox.org>
To:     André Almeida <andrealmeid@...lia.com>,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, wayland-devel@...ts.freedesktop.org
Cc:     pierre-eric.pelloux-prayer@....com,
        Pekka Paalanen <pekka.paalanen@...labora.com>,
        Daniel Vetter <daniel@...ll.ch>,
        'Marek Olšák' <maraeo@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Daniel Stone <daniel@...ishbar.org>, hwentlan@....com,
        Rob Clark <robdclark@...il.com>, ville.syrjala@...ux.intel.com,
        kernel-dev@...lia.com, alexander.deucher@....com,
        Dave Airlie <airlied@...il.com>, christian.koenig@....com,
        joshua@...ggi.es
Subject: Re: [PATCH v6 6/6] drm/doc: Define KMS atomic state set

On 8/15/23 20:57, André Almeida wrote:
> From: Pekka Paalanen <pekka.paalanen@...labora.com>
> 
> Specify how the atomic state is maintained between userspace and
> kernel, plus the special case for async flips.
> 
> Signed-off-by: Pekka Paalanen <pekka.paalanen@...labora.com>
> Signed-off-by: André Almeida <andrealmeid@...lia.com>

[...]

> +An atomic commit with the flag DRM_MODE_PAGE_FLIP_ASYNC is allowed to
> +effectively change only the FB_ID property on any planes. No-operation changes
> +are ignored as always. [...]

During the hackfest in Brno, it was mentioned that a commit which re-sets the same FB_ID could actually have an effect with VRR: It could trigger scanout of the next frame before vertical blank has reached its maximum duration. Some kind of mechanism is required for this in order to allow user space to perform low frame rate compensation.


-- 
Earthling Michel Dänzer            |                  https://redhat.com
Libre software enthusiast          |         Mesa and Xwayland developer