Re: [PATCH 10/22] drm/vkms: Introduce configfs for plane format

["José Expósito" <jose.exposito89@gmail.com>]

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@bootlin.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
>