[PATCH v2 09/16] drm/vkms: Allow to attach encoders and CRTCs via configfs

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

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

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           |  2 +
 drivers/gpu/drm/vkms/vkms_configfs.c | 55 ++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index e24767448775..650dbfa76f59 100644
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -106,6 +106,7 @@ Next, create one or more encoders::
 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
+  sudo ln -s /config/vkms/my-vkms/crtcs/crtc0 /config/vkms/my-vkms/encoders/encoder0/possible_crtcs
 
 Since at least one primary plane is required, make sure to set the right type::
 
@@ -122,6 +123,7 @@ 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 rm /config/vkms/my-vkms/encoders/*/possible_crtcs/*
   sudo rmdir /config/vkms/my-vkms/planes/*
   sudo rmdir /config/vkms/my-vkms/crtcs/*
   sudo rmdir /config/vkms/my-vkms/encoders/*
diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
index cf865728abc2..64aa10cd3156 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -70,11 +70,13 @@ struct vkms_configfs_crtc {
  *
  * @group: Top level configuration group that represents a encoder.
  * Initialized when a new directory is created under "/config/vkms/encoders"
+ * @possible_crtcs_group: Default subgroup of @group at "encoder/possible_crtcs"
  * @dev: The vkms_configfs_device this encoder belongs to
  * @config: Configuration of the VKMS encoder
  */
 struct vkms_configfs_encoder {
 	struct config_group group;
+	struct config_group possible_crtcs_group;
 	struct vkms_configfs_device *dev;
 	struct vkms_config_encoder *config;
 };
@@ -100,6 +102,10 @@ struct vkms_configfs_encoder {
 	container_of(to_config_group((item)), struct vkms_configfs_encoder, \
 		     group)
 
+#define encoder_possible_crtcs_item_to_vkms_configfs_encoder(item) \
+	container_of(to_config_group((item)), struct vkms_configfs_encoder, \
+		     possible_crtcs_group)
+
 static ssize_t crtc_writeback_show(struct config_item *item, char *page)
 {
 	struct vkms_configfs_crtc *crtc;
@@ -353,6 +359,49 @@ static const struct config_item_type plane_group_type = {
 	.ct_owner	= THIS_MODULE,
 };
 
+static int encoder_possible_crtcs_allow_link(struct config_item *src,
+					     struct config_item *target)
+{
+	struct vkms_configfs_encoder *encoder;
+	struct vkms_configfs_crtc *crtc;
+
+	if (target->ci_type != &crtc_item_type)
+		return -EINVAL;
+
+	encoder = encoder_possible_crtcs_item_to_vkms_configfs_encoder(src);
+	crtc = crtc_item_to_vkms_configfs_crtc(target);
+
+	guard(mutex)(&encoder->dev->lock);
+
+	if (encoder->dev->enabled)
+		return -EBUSY;
+
+	return vkms_config_encoder_attach_crtc(encoder->config, crtc->config);
+}
+
+static void encoder_possible_crtcs_drop_link(struct config_item *src,
+					     struct config_item *target)
+{
+	struct vkms_configfs_encoder *encoder;
+	struct vkms_configfs_crtc *crtc;
+
+	encoder = encoder_possible_crtcs_item_to_vkms_configfs_encoder(src);
+	crtc = crtc_item_to_vkms_configfs_crtc(target);
+
+	guard(mutex)(&encoder->dev->lock);
+	vkms_config_encoder_detach_crtc(encoder->config, crtc->config);
+}
+
+static struct configfs_item_operations encoder_possible_crtcs_item_operations = {
+	.allow_link	= encoder_possible_crtcs_allow_link,
+	.drop_link	= encoder_possible_crtcs_drop_link,
+};
+
+static const struct config_item_type encoder_possible_crtcs_group_type = {
+	.ct_item_ops	= &encoder_possible_crtcs_item_operations,
+	.ct_owner	= THIS_MODULE,
+};
+
 static void encoder_release(struct config_item *item)
 {
 	struct vkms_configfs_encoder *encoder;
@@ -402,6 +451,12 @@ static struct config_group *make_encoder_group(struct config_group *group,
 
 	config_group_init_type_name(&encoder->group, name, &encoder_item_type);
 
+	config_group_init_type_name(&encoder->possible_crtcs_group,
+				    "possible_crtcs",
+				    &encoder_possible_crtcs_group_type);
+	configfs_add_default_group(&encoder->possible_crtcs_group,
+				   &encoder->group);
+
 	return &encoder->group;
 }
 
-- 
2.48.1