drm/vkms: Allow to configure the plane type via configfs

When a plane is created, add a `type` file to allow to set the type:

 - 0 overlay
 - 1 primary
 - 2 cursor

Tested-by: Mark Yacoub <markyacoub@google.com>
Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
Co-developed-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Link: https://lore.kernel.org/r/20251016175618.10051-5-jose.exposito89@gmail.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

Documentation/gpu/vkms.rst

@@ -84,6 +84,11 @@ Start by creating one or more planes::
 
   sudo mkdir /config/vkms/my-vkms/planes/plane0
 
+Planes have 1 configurable attribute:
+
+- type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
+  exposed by the "type" property of a plane)
+
 Once you are done configuring the VKMS instance, enable it::
 
   echo "1" | sudo tee /config/vkms/my-vkms/enabled

drivers/gpu/drm/vkms/vkms_configfs.c

@@ -55,6 +55,51 @@ struct vkms_configfs_plane {
 #define plane_item_to_vkms_configfs_plane(item) \
 	container_of(to_config_group((item)), struct vkms_configfs_plane, group)
 
+static ssize_t plane_type_show(struct config_item *item, char *page)
+{
+	struct vkms_configfs_plane *plane;
+	enum drm_plane_type type;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	scoped_guard(mutex, &plane->dev->lock)
+		type = vkms_config_plane_get_type(plane->config);
+
+	return sprintf(page, "%u", type);
+}
+
+static ssize_t plane_type_store(struct config_item *item, const char *page,
+				size_t count)
+{
+	struct vkms_configfs_plane *plane;
+	enum drm_plane_type type;
+
+	plane = plane_item_to_vkms_configfs_plane(item);
+
+	if (kstrtouint(page, 10, &type))
+		return -EINVAL;
+
+	if (type != DRM_PLANE_TYPE_OVERLAY && type != DRM_PLANE_TYPE_PRIMARY &&
+	    type != DRM_PLANE_TYPE_CURSOR)
+		return -EINVAL;
+
+	scoped_guard(mutex, &plane->dev->lock) {
+		if (plane->dev->enabled)
+			return -EBUSY;
+
+		vkms_config_plane_set_type(plane->config, type);
+	}
+
+	return (ssize_t)count;
+}
+
+CONFIGFS_ATTR(plane_, type);
+
+static struct configfs_attribute *plane_item_attrs[] = {
+	&plane_attr_type,
+	NULL,
+};
+
 static void plane_release(struct config_item *item)
 {
 	struct vkms_configfs_plane *plane;
@@ -74,6 +119,7 @@ static struct configfs_item_operations plane_item_operations = {
 };
 
 static const struct config_item_type plane_item_type = {
+	.ct_attrs	= plane_item_attrs,
 	.ct_item_ops	= &plane_item_operations,
 	.ct_owner	= THIS_MODULE,
 };