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

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Date: Tue, 13 Feb 2024 11:04:40 +0200
From: Pekka Paalanen <pekka.paalanen@...oniitty.fi>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: 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>
Subject: Re: [PATCH 1/2] drm/tidss: Fix initial plane zpos values

On Tue, 13 Feb 2024 10:16:36 +0200
Tomi Valkeinen <tomi.valkeinen@...asonboard.com> wrote:

> When the driver sets up the zpos property it sets the default zpos value
> to the HW id of the plane. That is fine as such, but as on many DSS
> versions the driver arranges the DRM planes in a different order than
> the HW planes (to keep the non-scalable planes first), this leads to odd
> initial zpos values. An example is J721e, where the initial zpos values
> for DRM planes are 1, 3, 0, 2.
> 
> In theory the userspace should configure the zpos values properly when
> using multiple planes, and in that sense the initial zpos values
> shouldn't matter, but there's really no reason not to fix this and help
> the userspace apps which don't handle zpos perfectly. In particular,
> Weston seems to have issues dealing with the planes with the current
> default zpos values.
> 
> So let's change the zpos values for the DRM planes to 0, 1, 2, 3.
> 
> Another option would be to configure the planes marked as primary planes
> to zpos 0. On a two display system this would give us plane zpos values
> of 0, 0, 1, 2. The end result and behavior would be very similar in this
> option, and I'm not aware that this would actually help us in any way.
> So, to keep the code simple, I opted for the 0, 1, 2, 3 values.
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> Fixes: 32a1795f57ee ("drm/tidss: New driver for TI Keystone platform Display SubSystem")

Hi Tomi,

have you reported this to Weston? What exactly is the problem?

It doesn't seem like a good idea to work around userspace bugs
(non-regression, I presume?) with kernel changes.


Thanks,
pq

> ---
>  drivers/gpu/drm/tidss/tidss_plane.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/tidss/tidss_plane.c b/drivers/gpu/drm/tidss/tidss_plane.c
> index e1c0ef0c3894..68fed531f6a7 100644
> --- a/drivers/gpu/drm/tidss/tidss_plane.c
> +++ b/drivers/gpu/drm/tidss/tidss_plane.c
> @@ -213,7 +213,7 @@ struct tidss_plane *tidss_plane_create(struct tidss_device *tidss,
>  
>  	drm_plane_helper_add(&tplane->plane, &tidss_plane_helper_funcs);
>  
> -	drm_plane_create_zpos_property(&tplane->plane, hw_plane_id, 0,
> +	drm_plane_create_zpos_property(&tplane->plane, tidss->num_planes, 0,
>  				       num_planes - 1);
>  
>  	ret = drm_plane_create_color_properties(&tplane->plane,
> 


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