linux-kernel - Re: [PATCH v4 1/6] drm: allow DRM_MODE_PAGE_FLIP

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Date:   Wed, 5 Jul 2023 12:00:07 +0200
From:   Michel Dänzer <michel.daenzer@...lbox.org>
To:     Sebastian Wick <sebastian.wick@...hat.com>,
        André Almeida <andrealmeid@...lia.com>
Cc:     pierre-eric.pelloux-prayer@....com,
        Marek Olšák <maraeo@...il.com>,
        Italo Nicola <italonicola@...labora.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        wayland-devel@...ts.freedesktop.org,
        Pekka Paalanen <ppaalanen@...il.com>,
        dri-devel@...ts.freedesktop.org, kernel-dev@...lia.com,
        alexander.deucher@....com, hwentlan@....com,
        christian.koenig@....com, joshua@...ggi.es
Subject: Re: [PATCH v4 1/6] drm: allow DRM_MODE_PAGE_FLIP_ASYNC for atomic
 commits

On 7/4/23 19:06, Sebastian Wick wrote:
> On Sat, Jul 1, 2023 at 4:09 AM André Almeida <andrealmeid@...lia.com> wrote:
>>
>> @@ -949,6 +949,15 @@ struct hdr_output_metadata {
>>   * Request that the page-flip is performed as soon as possible, ie. with no
>>   * delay due to waiting for vblank. This may cause tearing to be visible on
>>   * the screen.
>> + *
>> + * When used with atomic uAPI, the driver will return an error if the hardware
>> + * doesn't support performing an asynchronous page-flip for this update.
>> + * User-space should handle this, e.g. by falling back to a regular page-flip.
>> + *
>> + * Note, some hardware might need to perform one last synchronous page-flip
>> + * before being able to switch to asynchronous page-flips. As an exception,
>> + * the driver will return success even though that first page-flip is not
>> + * asynchronous.
> 
> What would happen if one commits another async KMS update before the
> first page flip? Does one receive EAGAIN, does it amend the previous
> commit?

Should be the former. DRM_MODE_PAGE_FLIP_ASYNC just means the flip may complete outside of vertical blank, it doesn't change anything else.


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