linux-kernel - Re: [PATCH v3 17/33] drm/vkms: Introduce config for plane format

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Message-Id: <DF5NE3Y8O21F.1KKJWMX9JVXUP@bootlin.com>
Date: Tue, 23 Dec 2025 14:58:37 +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 v3 17/33] drm/vkms: Introduce config for plane format

On Mon Dec 22, 2025 at 11:11 AM CET, Louis Chauvet wrote:
> VKMS driver supports all the pixel formats for planes, but for testing it
> can be useful to only advertise few of them. This new configuration
> interface will allow configuring the pixel format per planes.
>
> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>

> --- a/drivers/gpu/drm/vkms/vkms_config.c
> +++ b/drivers/gpu/drm/vkms/vkms_config.c

> +void vkms_config_plane_remove_all_formats(struct vkms_config_plane *plane_cfg)
> +{
> +	plane_cfg->supported_formats_count = 0;

Why not kfree(plane_cfg->supported_formats) too? You will be (re)allocating
anyway if adding one or all formats later on, so the buffer you're not
freeing won't be reused anyway.

> +}
> +
> +void vkms_config_plane_remove_format(struct vkms_config_plane *plane_cfg, u32 drm_format)
> +{
> +	for (unsigned int i = 0; i < plane_cfg->supported_formats_count; i++) {
> +		if (plane_cfg->supported_formats[i] == drm_format) {
> +			plane_cfg->supported_formats[i] = plane_cfg->supported_formats[plane_cfg->supported_formats_count - 1];

I doubt these are less than 100 chars. ;-)

> --- a/drivers/gpu/drm/vkms/vkms_config.h
> +++ b/drivers/gpu/drm/vkms/vkms_config.h
> @@ -49,6 +49,8 @@ struct vkms_config {
>   * @supported_color_encodings: Color encodings that this plane will support
>   * @default_color_range: Default color range that should be used by this plane
>   * @supported_color_ranges: Color ranges that this plane will support
> + * @supported_formats: List of supported formats
> + * @supported_formats_count: Length of @supported_formats

Nitpick: this description is not adding much. "Number of elements in
@supported_formats" would be more useful, as it would clarify it's number
of (4-bytes) elements and not size in bytes.

> +int __must_check vkms_config_plane_add_format(struct vkms_config_plane *plane_cfg, u32 drm_format);
> +
> +/**
> + * vkms_config_plane_add_all_formats - Helper to quickly add all the supported formats
> + * @plane_cfg: Plane to add the formats to
> + *
> + * Returns: 0 on success, -ENOMEM if array allocation fails, -EINVAL if the format is not supported
> + * by VKMS

The "-EINVAL ... VKMS" part of the sentence does not apply here.

> +/**
> + * vkms_config_plane_remove_format - Remove a specific format from a plane
> + * @plane_cfg: Plane to remove the format to
                                             ^^ from

Luca

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