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

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Message-ID: <cec0fe4d-d244-d78b-ff70-e8dfba23070b@mailbox.org>
Date:   Thu, 17 Aug 2023 12:48:21 +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>,
        kernel-dev@...lia.com,
        'Marek Olšák' <maraeo@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Pekka Paalanen <ppaalanen@...il.com>, joshua@...ggi.es,
        alexander.deucher@....com, hwentlan@....com,
        christian.koenig@....com
Subject: Re: [PATCH v6 6/6] drm/doc: Define KMS atomic state set

On 8/17/23 12:37, Michel Dänzer wrote:
> 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.

That said, it doesn't make too much sense to use DRM_MODE_PAGE_FLIP_ASYNC for this, since it won't have any effect outside of vertical blank anyway.


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