Re: [PATCH 04/22] drm/vkms: Introduce configfs for plane rotation

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

On Sat, Oct 18, 2025 at 04:01:04AM +0200, Louis Chauvet wrote:
> To allows the userspace to test many hardware configuration, 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/gpu/vkms.rst           |  7 ++-
>  drivers/gpu/drm/vkms/vkms_configfs.c | 94 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 100 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index 3574e01b928d..a432968cc711 100644
> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -87,10 +87,15 @@ Start by creating one or more planes::
>  
>    sudo mkdir /config/vkms/my-vkms/planes/plane0
>  
> -Planes have 1 configurable attribute:
> +Planes have 3 configurable attribute:

s/attribute/attributes/

>  
>  - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
>    exposed by the "type" property of a 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 ea245e2e2fd2..450e45e66a45 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -322,10 +322,104 @@ static ssize_t plane_type_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);

Checkpatch is complaining about this line being 1 character longer than
it should... Feel free to ignore it:

WARNING: line length of 101 exceeds 100 columns
#58: FILE: drivers/gpu/drm/vkms/vkms_configfs.c:333:
+               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 ||
> +		    (val & vkms_config_plane_get_default_rotation(plane->config)) !=
> +		     vkms_config_plane_get_default_rotation(plane->config))
> +			return -EINVAL;

This makes a bit difficult to change the default supported rotations.

By default, default rotation is DRM_MODE_ROTATE_0. If the user wants to set the
supported rotations to DRM_MODE_REFLECT_X | DRM_MODE_REFLECT_Y | DRM_MODE_ROTATE_90,
this will fail because the default rotation is not included in the new set of
supported rotations.

Therefore, the user would need to add DRM_MODE_ROTATE_0 (DRM_MODE_REFLECT_X |
DRM_MODE_REFLECT_Y | DRM_MODE_ROTATE_90 | DRM_MODE_ROTATE_0), change the default rotation
to DRM_MODE_ROTATE_90 and drop DRM_MODE_ROTATE_0 from the supported rotations.

To avoid this, I think we should check this before enabling the device instead,
in vkms_config_is_valid().

Also, having this logic as a helper called by vkms_config_is_valid() allows to
add a KUnit test to make sure all cases are covered.

What do you think?


> +		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);
> +
> +	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;
> +	/* Should contains only one rotation */
> +	if (!is_power_of_2(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 ||
> +		    (val & vkms_config_plane_get_supported_rotations(plane->config)) != val)
> +			return -EINVAL;
> +
> +		vkms_config_plane_set_default_rotation(plane->config, val);
> +	}
> +
> +	return count;
> +}
> +
>  CONFIGFS_ATTR(plane_, type);
> +CONFIGFS_ATTR(plane_, supported_rotations);
> +CONFIGFS_ATTR(plane_, default_rotation);
>  
>  static struct configfs_attribute *plane_item_attrs[] = {
>  	&plane_attr_type,
> +	&plane_attr_supported_rotations,
> +	&plane_attr_default_rotation,
>  	NULL,
>  };
>  
> 
> -- 
> 2.51.0
>