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Message-ID: <aP8zbabbfLJ6F4Ok@fedora>
Date: Mon, 27 Oct 2025 09:55:09 +0100
From: José Expósito <jose.exposito89@...il.com>
To: Louis Chauvet <louis.chauvet@...tlin.com>
Cc: 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>, Jonathan Corbet <corbet@....net>,
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 10/22] drm/vkms: Introduce configfs for plane format
On Sat, Oct 18, 2025 at 04:01:10AM +0200, Louis Chauvet wrote:
> To allow the userspace to test many hardware configuration, introduce a
> new interface to configure the available formats per planes. VKMS supports
> multiple formats, so the userspace can choose any combination.
>
> The supported formats are configured by writing the fourcc code in
> supported_formats:
> # enable AR24 format
> echo '+AR24' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
> # disable AR24 format
> echo '-AR24' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
> # enable all format supported by VKMS
> echo '+*' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
> # disable all formats
> echo '-*' > /config/vkms/DEVICE_1/planes/PLANE_1/supported_formats
>
> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> ---
> Documentation/gpu/vkms.rst | 7 ++-
> drivers/gpu/drm/vkms/vkms_configfs.c | 82 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 88 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index 979f8a545498..deb14e7c48ea 100644
> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -87,7 +87,7 @@ Start by creating one or more planes::
>
> sudo mkdir /config/vkms/my-vkms/planes/plane0
>
> -Planes have 7 configurable attribute:
> +Planes have 8 configurable attribute:
>
> - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
> exposed by the "type" property of a plane)
> @@ -106,6 +106,11 @@ Planes have 7 configurable attribute:
> those exposed by the COLOR_RANGE property of a plane)
> - default_color_range: Default color range presented to the userspace, same
> values as supported_color_range
> +- supported_formats: List of supported formats for this plane. To add a new item in the
> + list, write it using a plus its fourcc code: +XR24
> + To remove a format, use a minus and its fourcc: -XR24
> + To add all formats use +*
> + To remove all formats, use -*
>
> Continue by creating one or more CRTCs::
>
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
> index 0b280c73b0cc..528f22fa2df1 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -599,6 +599,86 @@ static ssize_t plane_default_color_encoding_store(struct config_item *item,
> return count;
> }
>
> +static ssize_t plane_supported_formats_show(struct config_item *item, char *page)
> +{
> + struct vkms_configfs_plane *plane;
> +
> + plane = plane_item_to_vkms_configfs_plane(item);
> +
> + page[0] = '\0';
> +
> + scoped_guard(mutex, &plane->dev->lock)
> + {
This "{" should go in the same line.
> + u32 *formats = vkms_config_plane_get_supported_formats(plane->config);
> +
> + for (int i = 0;
> + i < vkms_config_plane_get_supported_formats_count(plane->config);
> + i++) {
> + char tmp[6] = { 0 };
> + const ssize_t ret = snprintf(tmp, ARRAY_SIZE(tmp), "%.*s\n",
> + (int)sizeof(*formats),
> + (char *)&formats[i]);
> + if (ret < 0)
> + return ret;
> + /*
> + * Limitation of ConfigFS attributes, an attribute can't be bigger
> + * than PAGE_SIZE. This will crop the result if this plane support
> + * more than ≈1000 formats.
> + */
> + if (ret + strlen(page) > PAGE_SIZE - 1)
> + return -ENOMEM;
> + strncat(page, tmp, ARRAY_SIZE(tmp));
> + }
> + }
> +
> + return strlen(page);
> +}
> +
> +static ssize_t plane_supported_formats_store(struct config_item *item,
> + const char *page, size_t count)
> +{
> + struct vkms_configfs_plane *plane;
> +
> + plane = plane_item_to_vkms_configfs_plane(item);
> + int ret = 0;
> + int ptr = 0;
> +
> + scoped_guard(mutex, &plane->dev->lock)
> + {
This "{" should go in the same line.
> + while (ptr < count) {
> + char tmp[4] = { ' ', ' ', ' ', ' ' };
> +
> + memcpy(tmp, &page[ptr + 1], min(sizeof(tmp), count - (ptr + 1)));
This is not handling correctly formats with less than 4 characters.
For example, "+R1" is not handled because it is adding the sctring NULL terminator
to tmp. I think you need to:
memcpy(tmp, &page[ptr + 1], min(sizeof(tmp), count - 1 - (ptr + 1)));
> + if (page[ptr] == '+') {
> + if (tmp[0] == '*') {
> + ret = vkms_config_plane_add_all_formats(plane->config);
> + if (ret)
> + return ret;
> + ptr += 1;
> + } else {
> + ret = vkms_config_plane_add_format(plane->config,
> + *(int *)tmp);
> + if (ret)
> + return ret;
> + ptr += 4;
> + }
> + } else if (page[ptr] == '-') {
> + if (tmp[0] == '*') {
> + vkms_config_plane_remove_all_formats(plane->config);
> + ptr += 1;
> + } else {
> + vkms_config_plane_remove_format(plane->config, *(int *)tmp);
> + ptr += 4;
> + }
> + }
> + /* Skip anything that is not a + or a - */
> + ptr += 1;
> + }
> + }
> +
> + return count;
> +}
> +
> CONFIGFS_ATTR(plane_, type);
> CONFIGFS_ATTR(plane_, supported_rotations);
> CONFIGFS_ATTR(plane_, default_rotation);
> @@ -606,6 +686,7 @@ CONFIGFS_ATTR(plane_, supported_color_range);
> CONFIGFS_ATTR(plane_, default_color_range);
> CONFIGFS_ATTR(plane_, supported_color_encoding);
> CONFIGFS_ATTR(plane_, default_color_encoding);
> +CONFIGFS_ATTR(plane_, supported_formats);
>
> static struct configfs_attribute *plane_item_attrs[] = {
> &plane_attr_type,
> @@ -615,6 +696,7 @@ static struct configfs_attribute *plane_item_attrs[] = {
> &plane_attr_default_color_range,
> &plane_attr_supported_color_encoding,
> &plane_attr_default_color_encoding,
> + &plane_attr_supported_formats,
> NULL,
> };
>
>
> --
> 2.51.0
>
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