Re: [PATCH RESEND v2 12/32] drm/vkms: Introduce configfs for plane color encoding

["Luca Ceresoli" <luca.ceresoli@bootlin.com>]

On Wed Oct 29, 2025 at 3:36 PM CET, Louis Chauvet wrote:
> To allows the userspace to test many hardware configuration, introduce a
> new interface to configure the available color encoding per planes. VKMS
> supports multiple color encoding, so the userspace can choose any
> combination.
>
> The supported color encoding are configured by writing a color encoding
> bitmask to the file `supported_color_encoding` and the default color
> encoding is chosen by writing a color encoding bitmask to
> `default_color_encoding`.
>
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---
>  Documentation/gpu/vkms.rst           |  7 ++-
>  drivers/gpu/drm/vkms/vkms_configfs.c | 98 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 104 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index eac1a942d6c4..dab6811687a2 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 4 configurable attributes:
> +Planes have 6 configurable attributes:
>
>  - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
>    exposed by the "type" property of a plane)
> @@ -97,6 +97,11 @@ Planes have 4 configurable attributes:
>    (same values as those exposed by the "rotation" property of a plane)
>  - default_rotation: Default rotation presented to the userspace, same values as
>    possible_rotations.
> +- supported_color_encoding: Available encoding for a plane, as a bitmask:
                                         encodings

> +  0x01 YCBCR_BT601, 0x02: YCBCR_BT709, 0x04 YCBCR_BT2020 (same values as those exposed
                           ^

Unintended colon? While I think it's nice to have, there is none elsewhere,
even in previous patches, and I'd say we can live happy without.

> +  by the COLOR_ENCODING property of a plane)
> +- default_color_encoding: Default color encoding presented to the userspace, same
> +  values as supported_color_encoding
>
>  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 7cc8ba315ef0..ee2e8d141f9e 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -439,16 +439,114 @@ static ssize_t plane_default_rotation_store(struct config_item *item,
>  	return count;
>  }
>
> +static ssize_t plane_supported_color_encodings_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +	unsigned int supported_color_encoding;
                     supported_color_encodings

> +
> +	plane = plane_item_to_vkms_configfs_plane(item);

As for patch 9, for consistency:

  struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);

> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		supported_color_encoding = vkms_config_plane_get_supported_color_encodings(plane->config);
> +	}
> +
> +	return sprintf(page, "%u", supported_color_encoding);
> +}
> +
> +static ssize_t plane_supported_color_encodings_store(struct config_item *item,
> +						     const char *page, size_t count)
> +{
> +	struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);
> +	int ret, val = 0;
> +
> +	ret = kstrtouint(page, 10, &val);
> +	if (ret)
> +		return ret;
> +
> +	/* Should be a supported value */
> +	if (val & ~(BIT(DRM_COLOR_YCBCR_BT601) |
> +		    BIT(DRM_COLOR_YCBCR_BT709) |
> +		    BIT(DRM_COLOR_YCBCR_BT2020)))
> +		return -EINVAL;
> +	/* Should at least provide one color range */
> +	if ((val & (BIT(DRM_COLOR_YCBCR_BT601) |
> +		    BIT(DRM_COLOR_YCBCR_BT709) |
> +		    BIT(DRM_COLOR_YCBCR_BT2020))) == 0)

I'm mentioning here as it comes to mind, but it's valid for other similar
patches in this series: why not adding a

  #define DRM_COLOR_ENCODINGS_SUPPORTED ( \
                   BIT(DRM_COLOR_YCBCR_BT601) |
                   BIT(DRM_COLOR_YCBCR_BT709) |
                   BIT(DRM_COLOR_YCBCR_BT2020))

and use it in place of the various bitwise-or sequences?

This would simplify work later on if adding a new color encoding (or color
range, or...).

Somewhat like DRM_MODE_*_MASK.

> +		return -EINVAL;
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		/* Ensures that the default rotation is included in supported rotation */
> +		if (plane->dev->enabled)
> +			return -EINVAL;

And here the comment is definitely wrong. :-)

> +
> +		vkms_config_plane_set_supported_color_encodings(plane->config, val);
> +	}
> +
> +	return count;
> +}
> +
> +/* Plane default_color_encoding : vkms/<device>/planes/<plane>/default_color_encoding */

There's no such comment in other places, so for consistency remove it (or
add it everywhere?!? ... no, just kidding).

> +
> +static ssize_t plane_default_color_encoding_show(struct config_item *item, char *page)
> +{
> +	struct vkms_configfs_plane *plane;
> +	unsigned int default_color_encoding;
> +
> +	plane = plane_item_to_vkms_configfs_plane(item);
> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		default_color_encoding = vkms_config_plane_get_default_color_encoding(plane->config);
> +	}
> +
> +	return sprintf(page, "%u", default_color_encoding);
> +}
> +
> +static ssize_t plane_default_color_encoding_store(struct config_item *item,
> +						  const char *page, size_t count)
> +{
> +	struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);
> +	int ret, val = 0;
> +
> +	ret = kstrtouint(page, 10, &val);
> +	if (ret)
> +		return ret;
> +
> +	/* Should be a supported value */
> +	if (val & ~(BIT(DRM_COLOR_YCBCR_BT601) |
> +		    BIT(DRM_COLOR_YCBCR_BT709) |
> +		    BIT(DRM_COLOR_YCBCR_BT2020)))
> +		return -EINVAL;
> +	/* Should at least provide one color range */
> +	if ((val & (BIT(DRM_COLOR_YCBCR_BT601) |
> +		    BIT(DRM_COLOR_YCBCR_BT709) |
> +		    BIT(DRM_COLOR_YCBCR_BT2020))) == 0)
> +		return -EINVAL;

Shouldn't you check that exactly one bit is set? As in patch 9.

> +
> +	scoped_guard(mutex, &plane->dev->lock) {
> +		/* Ensures that the default rotation is included in supported rotation */
> +		if (plane->dev->enabled)
> +			return -EINVAL;

As before, wrong comment.

Luca

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