[PATCH v3 10/33] drm/vkms: Introduce configfs for plane rotation

Louis Chauvet
2025-12-22T10:11:43Z

To allows the userspace to test many hardware configurations, introduce a
new interface to configure the available rotation per planes. VKMS
supports any rotation and reflection, so the userspace can choose any
combination.

The supported rotations are configured by writing a rotation bitmask to
the file `supported_rotations` and the default rotation is chosen by
writing a rotation bitmask to `default_rotation`.

Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
---
Documentation/ABI/testing/configfs-vkms | 15 ++++++
Documentation/gpu/vkms.rst | 7 ++-
drivers/gpu/drm/vkms/vkms_configfs.c | 93 ++++++++++++++++++++++++++++++---
3 files changed, 108 insertions(+), 7 deletions(-)

diff --git a/Documentation/ABI/testing/configfs-vkms b/Documentation/ABI/testing/configfs-vkms
index 6fe375d1636f..9b74375bbf35 100644
--- a/Documentation/ABI/testing/configfs-vkms
+++ b/Documentation/ABI/testing/configfs-vkms
@@ -109,6 +109,21 @@ Contact: dri-devel@lists.freedesktop.org
Description:
Name of the plane.

+What: /sys/kernel/config/vkms/<device>/planes/<plane>/possible_rotations
+Date: Nov 2025
+Contact: dri-devel@lists.freedesktop.org
+Description:
+ Available rotations for the plane, as a bitmask:
+ 0x01 - no rotation, 0x02 - rotate 90°, 0x04 - rotate 180°,
+ 0x08 - rotate 270°, 0x10 - reflect x, 0x20 - reflect y.
+
+What: /sys/kernel/config/vkms/<device>/planes/<plane>/default_rotation
+Date: Nov 2025
+Contact: dri-devel@lists.freedesktop.org
+Description:
+ Default rotation presented to userspace, same values as
+ possible_rotations.
+
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 79f1185d8645..7fd746dd6ee2 100644
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -87,11 +87,16 @@ Start by creating one or more planes::

sudo mkdir /config/vkms/my-vkms/planes/plane0

-Planes have 2 configurable attributes:
+Planes have 4 configurable attributes:

- type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
exposed by the "type" property of a plane)
- name: Name of the plane. Allowed characters are [A-Za-z1-9_-]
+- possible_rotations: Available rotation for a plane, as a bitmask: 0x01 no rotation,
+ 0x02 rotate 90°, 0x04 rotate 180°, 0x08 rotate 270°, 0x10 reflect x, 0x20 reflect y
+ (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.

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 989788042191..bcc3e222e6b3 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -365,24 +365,105 @@ static ssize_t plane_name_store(struct config_item *item, const char *page,
return (ssize_t)count;
}

+static ssize_t plane_supported_rotations_show(struct config_item *item, char *page)
+{
+ struct vkms_configfs_plane *plane;
+ unsigned int plane_supported_rotations;
+
+ plane = plane_item_to_vkms_configfs_plane(item);
+
+ scoped_guard(mutex, &plane->dev->lock) {
+ plane_supported_rotations = vkms_config_plane_get_supported_rotations(plane->config);
+ }
+
+ return sprintf(page, "%u", plane_supported_rotations);
+}
+
+static ssize_t plane_supported_rotations_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, 0, &val);
+ if (ret)
+ return ret;
+
+ /* Should be a supported value */
+ if (val & ~(DRM_MODE_ROTATE_MASK | DRM_MODE_REFLECT_MASK))
+ return -EINVAL;
+ /* Should at least provide one rotation */
+ if (!(val & DRM_MODE_ROTATE_MASK))
+ return -EINVAL;
+
+ scoped_guard(mutex, &plane->dev->lock) {
+ if (plane->dev->enabled)
+ return -EBUSY;
+
+ vkms_config_plane_set_supported_rotations(plane->config, val);
+ }
+
+ return count;
+}
+
+static ssize_t plane_default_rotation_show(struct config_item *item, char *page)
+{
+ struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);
+ unsigned int plane_default_rotation;
+
+ scoped_guard(mutex, &plane->dev->lock) {
+ plane_default_rotation = vkms_config_plane_get_default_rotation(plane->config);
+ }
+
+ return sprintf(page, "%u", plane_default_rotation);
+}
+
+static ssize_t plane_default_rotation_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 & ~(DRM_MODE_ROTATE_MASK | DRM_MODE_REFLECT_MASK))
+ return -EINVAL;
+
+ /* Should contain exactly one rotation */
+ if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK))
+ return -EINVAL;
+
+ scoped_guard(mutex, &plane->dev->lock) {
+ if (plane->dev->enabled)
+ return -EBUSY;
+
+ vkms_config_plane_set_default_rotation(plane->config, val);
+ }
+
+ return count;
+}
+
CONFIGFS_ATTR(plane_, type);
CONFIGFS_ATTR(plane_, name);
+CONFIGFS_ATTR(plane_, supported_rotations);
+CONFIGFS_ATTR(plane_, default_rotation);

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

static void plane_release(struct config_item *item)
{
- struct vkms_configfs_plane *plane;
- struct mutex *lock;
-
- plane = plane_item_to_vkms_configfs_plane(item);
- lock = &plane->dev->lock;
+ struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);

- scoped_guard(mutex, lock) {
+ scoped_guard(mutex, &plane->dev->lock) {
vkms_config_destroy_plane(plane->config);
kfree(plane);
}

--
2.51.2