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

[Tomi Valkeinen]

Hi,

On 13/02/2024 13:39, Daniel Stone wrote:
> Hi,
>
> On Tue, 13 Feb 2024 at 10:18, Marius Vlad <marius.vlad@xxxxxxxxxxxxx> 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.

Yeah, that's always a worry. I do hope that no user of tidss expects the 
plane zpos values to be the current funny ones. But we'll probably find 
out when I merge this =).

> > > 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. ;)

Hmm, so do I understand it right, the plane code from 12 years back 
supposedly works ok, but somewhere around Weston 10 something broke, but 
was fixed with the commits you mention above?

 Tomi