[PATCH v2 07/16] drm/vkms: Allow to attach planes and CRTCs via configfs

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

Create a default subgroup at /config/vkms/planes/plane/possible_crtcs
that will contain symbolic links to the possible CRTCs for the plane.

Co-developed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
---
 Documentation/gpu/vkms.rst           |  9 +++++
 drivers/gpu/drm/vkms/vkms_configfs.c | 54 ++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index abe7a0f5a4ab..13b96837a266 100644
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -98,6 +98,14 @@ CRTCs have 1 configurable attribute:
 
 - writeback: Enable or disable writeback connector support by writing 1 or 0
 
+To finish the configuration, link the different pipeline items::
+
+  sudo ln -s /config/vkms/my-vkms/crtcs/crtc0 /config/vkms/my-vkms/planes/plane0/possible_crtcs
+
+Since at least one primary plane is required, make sure to set the right type::
+
+  echo "1" | sudo tee /config/vkms/my-vkms/planes/plane0/type
+
 Once you are done configuring the VKMS instance, enable it::
 
   echo "1" | sudo tee /config/vkms/my-vkms/enabled
@@ -108,6 +116,7 @@ Finally, you can remove the VKMS instance disabling it::
 
 And removing the top level directory and its subdirectories::
 
+  sudo rm /config/vkms/my-vkms/planes/*/possible_crtcs/*
   sudo rmdir /config/vkms/my-vkms/planes/*
   sudo rmdir /config/vkms/my-vkms/crtcs/*
   sudo rmdir /config/vkms/my-vkms
diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
index 233a3d4ad75c..09d1f2224d01 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -38,11 +38,13 @@ struct vkms_configfs_device {
  *
  * @group: Top level configuration group that represents a plane.
  * Initialized when a new directory is created under "/config/vkms/planes"
+ * @possible_crtcs_group: Default subgroup of @group at "plane/possible_crtcs"
  * @dev: The vkms_configfs_device this plane belongs to
  * @config: Configuration of the VKMS plane
  */
 struct vkms_configfs_plane {
 	struct config_group group;
+	struct config_group possible_crtcs_group;
 	struct vkms_configfs_device *dev;
 	struct vkms_config_plane *config;
 };
@@ -71,6 +73,10 @@ struct vkms_configfs_crtc {
 #define plane_item_to_vkms_configfs_plane(item) \
 	container_of(to_config_group((item)), struct vkms_configfs_plane, group)
 
+#define plane_possible_crtcs_item_to_vkms_configfs_plane(item) \
+	container_of(to_config_group((item)), struct vkms_configfs_plane, \
+		     possible_crtcs_group)
+
 #define crtc_item_to_vkms_configfs_crtc(item) \
 	container_of(to_config_group((item)), struct vkms_configfs_crtc, group)
 
@@ -175,6 +181,49 @@ static const struct config_item_type crtc_group_type = {
 	.ct_owner	= THIS_MODULE,
 };
 
+static int plane_possible_crtcs_allow_link(struct config_item *src,
+					   struct config_item *target)
+{
+	struct vkms_configfs_plane *plane;
+	struct vkms_configfs_crtc *crtc;
+
+	if (target->ci_type != &crtc_item_type)
+		return -EINVAL;
+
+	plane = plane_possible_crtcs_item_to_vkms_configfs_plane(src);
+	crtc = crtc_item_to_vkms_configfs_crtc(target);
+
+	guard(mutex)(&plane->dev->lock);
+
+	if (plane->dev->enabled)
+		return -EBUSY;
+
+	return vkms_config_plane_attach_crtc(plane->config, crtc->config);
+}
+
+static void plane_possible_crtcs_drop_link(struct config_item *src,
+					   struct config_item *target)
+{
+	struct vkms_configfs_plane *plane;
+	struct vkms_configfs_crtc *crtc;
+
+	plane = plane_possible_crtcs_item_to_vkms_configfs_plane(src);
+	crtc = crtc_item_to_vkms_configfs_crtc(target);
+
+	guard(mutex)(&plane->dev->lock);
+	vkms_config_plane_detach_crtc(plane->config, crtc->config);
+}
+
+static struct configfs_item_operations plane_possible_crtcs_item_operations = {
+	.allow_link	= plane_possible_crtcs_allow_link,
+	.drop_link	= plane_possible_crtcs_drop_link,
+};
+
+static const struct config_item_type plane_possible_crtcs_group_type = {
+	.ct_item_ops	= &plane_possible_crtcs_item_operations,
+	.ct_owner	= THIS_MODULE,
+};
+
 static ssize_t plane_type_show(struct config_item *item, char *page)
 {
 	struct vkms_configfs_plane *plane;
@@ -267,6 +316,11 @@ static struct config_group *make_plane_group(struct config_group *group,
 
 	config_group_init_type_name(&plane->group, name, &plane_item_type);
 
+	config_group_init_type_name(&plane->possible_crtcs_group,
+				    "possible_crtcs",
+				    &plane_possible_crtcs_group_type);
+	configfs_add_default_group(&plane->possible_crtcs_group, &plane->group);
+
 	return &plane->group;
 }
 
-- 
2.48.1