linux-kernel - Re: [PATCH 1/2] drm/tidss: Fix initial plane zpos values

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Date: Tue, 13 Feb 2024 11:39:53 +0000
From: Daniel Stone <daniel@...ishbar.org>
To: Marius Vlad <marius.vlad@...labora.com>
Cc: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, 
	Pekka Paalanen <pekka.paalanen@...oniitty.fi>, Jyri Sarha <jyri.sarha@....fi>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Sam Ravnborg <sam@...nborg.org>, Devarsh Thakkar <devarsht@...com>, Aradhya Bhatia <a-bhatia1@...com>, 
	Francesco Dolcini <francesco@...cini.it>, Tomi Valkeinen <tomi.valkeinen@...com>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	"wayland-devel@...ts.freedesktop.org" <wayland-devel@...ts.freedesktop.org>, Randolph Sapp <rs@...com>
Subject: Re: [PATCH 1/2] drm/tidss: Fix initial plane zpos values

Hi,

On Tue, 13 Feb 2024 at 10:18, Marius Vlad <marius.vlad@...labora.com> wrote:
> On Tue, Feb 13, 2024 at 11:57:59AM +0200, Tomi Valkeinen wrote:
> > I haven't. I'm quite unfamiliar with Weston, and Randolph from TI (cc'd) has
> > been working on the Weston side of things. I also don't know if there's
> > something TI specific here, as the use case is with non-mainline GPU drivers
> > and non-mainline Mesa. I should have been a bit clearer in the patch
> > description, as I didn't mean that upstream Weston has a bug (maybe it has,
> > maybe it has not).

Don't worry about it. We've had bugs in the past and I'm sure we'll
have more. :) Either way, it's definitely better to have the kernel
expose sensible behaviour rather than weird workarounds, unless
they've been around for so long that they're basically baked into ABI.

> > The issue seen is that when Weston decides to use DRM planes for
> > composition, the plane zpositions are not configured correctly (or at all?).
> > Afaics, this leads to e.g. weston showing a window with a DRM "overlay"
> > plane that is behind the "primary" root plane, so the window is not visible.
> > And as Weston thinks that the area supposedly covered by the overlay plane
> > does not need to be rendered on the root plane, there are also artifacts on
> > that area.
> >
> > Also, the Weston I used is a bit older one (10.0.1), as I needed to go back
> > in my buildroot versions to get all that non-mainline GPU stuff compiled and
> > working. A more recent Weston may behave differently.
>
> Right after Weston 10, we had a few minor changes related to the
> zpos-sorting list of planes and how we parse the plan list without having
> a temporary zpos ordered list to pick planes from.
>
> And there's another fix for missing out to set out the zpos for scanout
> to the minimum available - which seems like a good candidate to explain
> what happens in the issue described above. So if trying Weston again,
> please try with at least Weston 12, which should have those changes
> in.

Specifically, you probably want commits 4cde507be6a1 and 58dde0e0c000.
I think the window of breakage was small enough that - assuming either
those commits or an upgrade to Weston 12/13 fixes it - we can just ask
people to upgrade to a fixed Weston.

> > Presuming this is not related to any TI specific code, I guess it's a
> > regression in the sense that at some point Weston added the support to use
> > planes for composition, so previously with only a single plane per display
> > there was no issue.

That point was 12 years ago, so not that novel. ;)

Cheers,
Daniel