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

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Message-ID: <20180420142533.GN5671@atomide.com>
Date:   Fri, 20 Apr 2018 07:25:33 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Daniel Stone <daniel@...ishbar.org>
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,

* Daniel Stone <daniel@...ishbar.org> [180420 10:21]:
> Hi Tomi,
> 
> 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?

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 can easily test patches though with a command mode LCD and normal
HDMI setup on droid 4.

Regards,

Tony

[0] https://lists.x.org/archives/xorg-devel/2018-February/055890.html