linux-kernel - Re: [PATCHv3 3/8] drm/omap: add support for manually updated displays

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Message-ID: <CAPj87rPLEEa6_13T38BQM4HXV5v17MzjGmLE2WSPJTo09qUJpQ@mail.gmail.com>
Date:   Fri, 20 Apr 2018 15:39:20 +0100
From:   Daniel Stone <daniel@...ishbar.org>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Tomi Valkeinen <tomi.valkeinen@...com>,
        Sebastian Reichel <sebastian.reichel@...labora.co.uk>,
        Sebastian Reichel <sre@...nel.org>,
        Pavel Machek <pavel@....cz>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree@...r.kernel.org, linux-omap@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel@...labora.com
Subject: Re: [PATCHv3 3/8] drm/omap: add support for manually updated displays

Hi Tony!

On 20 April 2018 at 15:25, Tony Lindgren <tony@...mide.com> wrote:
> * Daniel Stone <daniel@...ishbar.org> [180420 10:21]:
>> On 20 April 2018 at 08:09, Tomi Valkeinen <tomi.valkeinen@...com> wrote:
>> > It's actually not quite clear to me how manual update displays work with
>> > DRM...
>> >
>> > As far as I see, we have essentially two cases: 1) single buffering,
>> > where the userspace must set an area in the fb dirty, which then
>> > triggers the update, 2) multi buffering, which doesn't need fb dirty,
>> > but just a page flip which triggers the update.
>> >
>> > In the 2) case (which I think is the optimal case which all the modern
>> > apps should use), there's no need for delayed work or any work, and the
>> > code flow should be very similar to the auto-update model.
>>
>> Correct. There's been talk (and I think patches?) of adding a
>> per-plane dirty property, so userspace can as an optimisation inform
>> the kernel of the area changed between frames. But short of that, a
>> pageflip needs to trigger a full-plane update, with no dirtyfb
>> required.
>
> For per-plane dirty property patches, which ones do you refer to?

Here's the latest iteration of that series:
https://lists.freedesktop.org/archives/dri-devel/2018-April/171900.html
<1522885748-67122-1-git-send-email-drawat@...are.com>

> Then for xorg, there's my second attempt on fixing the command mode
> rotation at [0]. Not sure if that's enough for a fix?
>
> It seems not very efficient to me and I don't really know where
> the the per crtc dirty flag should be stored..

I try to deny all knowledge of X11 these days, I'm afraid.

Cheers,
Daniel