[PATCH v3 13/33] drm/vkms: Introduce configfs for plane color encoding

Louis Chauvet
2025-12-22T10:11:54Z

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/ABI/testing/configfs-vkms | 14 +++++
Documentation/gpu/vkms.rst | 8 ++-
drivers/gpu/drm/vkms/vkms_configfs.c | 97 +++++++++++++++++++++++++++++++++
3 files changed, 118 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/configfs-vkms b/Documentation/ABI/testing/configfs-vkms
index 9b74375bbf35..242aae91289c 100644
--- a/Documentation/ABI/testing/configfs-vkms
+++ b/Documentation/ABI/testing/configfs-vkms
@@ -124,6 +124,20 @@ Description:
Default rotation presented to userspace, same values as
possible_rotations.

+What: /sys/kernel/config/vkms/<device>/planes/<plane>/supported_color_encoding
+Date: Nov 2025
+Contact: dri-devel@lists.freedesktop.org
+Description:
+ Available color encodings for the plane, as a bitmask:
+ 0x01 - YCBCR_BT601, 0x02 - YCBCR_BT709, 0x04 - YCBCR_BT2020.
+
+What: /sys/kernel/config/vkms/<device>/planes/<plane>/default_color_encoding
+Date: Nov 2025
+Contact: dri-devel@lists.freedesktop.org
+Description:
+ Default color encoding presented to userspace, same
+ values as supported_color_encoding.
+
What: /sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
Date: Nov 2025
Contact: dri-devel@lists.freedesktop.org
diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index 7fd746dd6ee2..0d4dae3ba8e5 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 +97,12 @@ 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_encodings: Available encodings for a plane, as a bitmask:
+ 0x01 YCBCR_BT601, 0x02 YCBCR_BT709, 0x04 YCBCR_BT2020 (same values as those exposed
+ by the COLOR_ENCODING property of a plane). If set, supported_color_range
+ must be set too.
+- default_color_encoding: Default color encoding presented to the userspace, same
+ values as supported_color_encodings

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 bcc3e222e6b3..755978b17c95 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -9,6 +9,14 @@
#include "vkms_configfs.h"
#include "vkms_connector.h"

+/**
+ * VKMS_SUPPORTED_COLOR_ENCODINGS - Bitmask of all supported color encodings in VKMS
+ */
+#define VKMS_SUPPORTED_COLOR_ENCODINGS ( \
+ BIT(DRM_COLOR_YCBCR_BT601) | \
+ BIT(DRM_COLOR_YCBCR_BT709) | \
+ BIT(DRM_COLOR_YCBCR_BT2020))
+
/* To avoid registering configfs more than once or unregistering on error */
static bool is_configfs_registered;

@@ -446,16 +454,105 @@ 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 = plane_item_to_vkms_configfs_plane(item);
+ unsigned int supported_color_encodings;
+
+ scoped_guard(mutex, &plane->dev->lock)
+ supported_color_encodings = vkms_config_plane_get_supported_color_encodings(plane->config);
+
+ return sprintf(page, "%u", supported_color_encodings);
+}
+
+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 & ~(VKMS_SUPPORTED_COLOR_ENCODINGS))
+ return -EINVAL;
+ /* Should at least provide one color range */
+ if ((val & (VKMS_SUPPORTED_COLOR_ENCODINGS)) == 0)
+ return -EINVAL;
+
+ scoped_guard(mutex, &plane->dev->lock) {
+ if (plane->dev->enabled)
+ return -EBUSY;
+
+ vkms_config_plane_set_supported_color_encodings(plane->config, val);
+ }
+
+ return count;
+}
+
+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 = BIT(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 & ~VKMS_SUPPORTED_COLOR_ENCODINGS)
+ return -EINVAL;
+ /* Should at least provide one color range */
+ if ((val & VKMS_SUPPORTED_COLOR_ENCODINGS) == 0)
+ return -EINVAL;
+
+ /* Ensure val is a single bit set */
+ if (!is_power_of_2(val))
+ return -EINVAL;
+
+ /* Convert bit position to the proper enum value */
+ val = __ffs(val) + DRM_COLOR_YCBCR_BT601;
+
+ scoped_guard(mutex, &plane->dev->lock) {
+ if (plane->dev->enabled)
+ return -EBUSY;
+
+ vkms_config_plane_set_default_color_encoding(plane->config, val);
+ }
+
+ return count;
+}
+
CONFIGFS_ATTR(plane_, type);
CONFIGFS_ATTR(plane_, name);
CONFIGFS_ATTR(plane_, supported_rotations);
CONFIGFS_ATTR(plane_, default_rotation);
+CONFIGFS_ATTR(plane_, supported_color_encodings);
+CONFIGFS_ATTR(plane_, default_color_encoding);

static struct configfs_attribute *plane_item_attrs[] = {
&plane_attr_type,
&plane_attr_name,
&plane_attr_supported_rotations,
&plane_attr_default_rotation,
+ &plane_attr_supported_color_encodings,
+ &plane_attr_default_color_encoding,
NULL,
};

--
2.51.2