Re: [PATCH RESEND v2 09/32] drm/vkms: Introduce configfs for plane rotation

Luca Ceresoli
2025-12-18T17:59:11Z

On Wed Oct 29, 2025 at 3:36 PM CET, Louis Chauvet wrote:
> To allows the userspace to test many hardware configuration, introduce a
configurations

> 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/gpu/vkms.rst | 7 ++-
> drivers/gpu/drm/vkms/vkms_configfs.c | 91 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 97 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index 1fe6e420c963..eac1a942d6c4 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
> +- 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 be6c3ba998b9..7cc8ba315ef0 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -352,12 +352,103 @@ 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);

Small nit: below you do

struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);

Why not here as well?

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

The comment does not seem related to the code.

> +
> + 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;
> + unsigned int plane_default_rotation;
> +
> + plane = plane_item_to_vkms_configfs_plane(item);

Same as above.

> +
> + 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 at least provide one rotation */
> + if ((val & DRM_MODE_ROTATE_MASK) == 0)
> + return -EINVAL;

This if is redundant because...

> + /* Should contains only one rotation */
/* Should contain exactly one rotation */

> + if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK))
> + return -EINVAL;

...is_power_of_2() returns false if the parameter is 0.

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

Same as above.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering