linux-kernel - Re: [PATCH RESEND v2 20/32] drm/vkms: Introduce configfs for plane zpos property

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Message-Id: <DF2CXCN54ZCQ.2556SL3J03DOO@bootlin.com>
Date: Fri, 19 Dec 2025 18:08:33 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Louis Chauvet" <louis.chauvet@...tlin.com>, "Haneen Mohammed"
 <hamohammed.sa@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Melissa Wen"
 <melissa.srw@...il.com>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>, "David Airlie"
 <airlied@...il.com>, <jose.exposito89@...il.com>, "Jonathan Corbet"
 <corbet@....net>
Cc: <victoria@...tem76.com>, <sebastian.wick@...hat.com>,
 <thomas.petazzoni@...tlin.com>, <dri-devel@...ts.freedesktop.org>,
 <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>
Subject: Re: [PATCH RESEND v2 20/32] drm/vkms: Introduce configfs for plane
 zpos property

On Wed Oct 29, 2025 at 3:36 PM CET, Louis Chauvet wrote:
> Modern compositor rely on zpos management to offload some processing to
> deticated hardware. In order to test multiple configurations, add zpos
> configuration to configFS.
>
> Introduce multiple attributes to configure zpos:
> - zpos_enabled - Create or not the zpos property. If not created, the zpos
>   is undefined.
> - zpos_mutable - If the zpos property is created, allow or not the
>   userspace to modify it
> - zpos_initial - Initial value for zpos property. Must be between zpos_min
>   and zpos_max
> - zpos_min - Minimal zpos value for this plane. Must be smaller than or
               Minimum

>   equals to zpos_max
    equal

or, more simply:

  - zpos_min - Minimal zpos value for this plane. Must be <= zpos_max

> - zpos_max - Maximal zpos value for this plane. Must be greater than or
               Maximum

>   equals to zpos_min

As above

> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst

> @@ -114,6 +114,13 @@ Planes have 9 configurable attributes:
>    To remove a format, use a minus and its fourcc: -XR24
>    To add all formats use +*
>    To remove all formats, use -*
> +- zpos_enabled: Enable or not the zpos property: 1 enable, 0 disable
> +- zpos_mutable: Create the zpos property as a mutable or imutable property: 1 mutable,
> +  0 disable. No effect if zpos_enabled is not set.

s/disable/immutable/

> +- zpos_initial: Set the initial zpos value. Must be between zpos_min and zpos_max. No
> +  effect if zpos_enabled is not set.
> +- zpos_min: Set the minimal zpos value. No effect if zpos_enabled is not set.
                       minimum

> +- zpos_max: Set the maximal zpos value. No effect if zpos_enabled is not set.
                       maximum

With those fixed:

 Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>


--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com