linux-kernel - Re: [PATCH] drm: add capability DRM_CAP_ASYNC

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Message-ID: <fb45217c-d9ad-b208-d55d-51299ead108b@daenzer.net>
Date:   Thu, 20 Dec 2018 18:16:52 +0100
From:   Michel Dänzer <michel@...nzer.net>
To:     Daniel Vetter <daniel@...ll.ch>,
        Alex Deucher <alexdeucher@...il.com>
Cc:     dnicoara@...omium.org,
        Stéphane Marchesin <marcheu@...gle.com>,
        Sean Paul <seanpaul@...gle.com>,
        Alexandros Frantzis <alexandros.frantzis@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Helen Koike <helen.koike@...labora.com>, kernel@...labora.com,
        "Kazlauskas, Nicholas" <nicholas.kazlauskas@....com>
Subject: Re: [PATCH] drm: add capability DRM_CAP_ASYNC_UPDATE

On 2018-12-20 6:09 p.m., Daniel Vetter wrote:
> On Thu, Dec 20, 2018 at 6:03 PM Alex Deucher <alexdeucher@...il.com> wrote:
>> On Thu, Dec 20, 2018 at 11:54 AM Daniel Vetter <daniel@...ll.ch> wrote:
> 
>>> Not sure about the gamma thing since we had opposite bugs on i915
>>> about gamma not being vsynced and tearing terribly. Cursor is special
>>> since it tends to be too small to notice tearing.
>>
>> Our cursor hw (and possibly gamma as well Nicholas?  Harry?) is double
>> buffered, so we can update it any time for the most part and the
>> changes won't take affect until the next vupdate period.
> 
> Hm, I guess we could make the gamma update optionally async, and let
> drivers deal. The issue is that the current async helper stuff won't
> cope with gamma updates (it's aimed at plane updates only, not at crtc
> property updates). Or we get userspace to do proper atomic updates. Or
> we do some faking in the kernel, e.g. waiting with the gamma update
> until the next atomic update happens. But that kinda breaks
> ->atomic_check.

Would it be possible to merge gamma changes into a pending commit, if
there is one, and create a new commit otherwise?

Otherwise the atomic API just moves this same problem to be solved by
userspace.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer