drm/vkms: Allow to configure multiple CRTCs via configfs

Create a default subgroup at /config/vkms/crtcs to allow to create as
many CRTCs as required.

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/20251016175618.10051-6-jose.exposito89@gmail.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

Documentation/gpu/vkms.rst

@@ -74,6 +74,7 @@ By default, the instance is disabled::
 And directories are created for each configurable item of the display pipeline::
 
   tree /config/vkms/my-vkms
+  ├── crtcs
   ├── enabled
   └── planes
 
@@ -89,6 +90,10 @@ 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)
 
+Continue by creating one or more CRTCs::
+
+  sudo mkdir /config/vkms/my-vkms/crtcs/crtc0
+
 Once you are done configuring the VKMS instance, enable it::
 
   echo "1" | sudo tee /config/vkms/my-vkms/enabled
@@ -100,6 +105,7 @@ Finally, you can remove the VKMS instance disabling it::
 And removing the top level directory and its subdirectories::
 
   sudo rmdir /config/vkms/my-vkms/planes/*
+  sudo rmdir /config/vkms/my-vkms/crtcs/*
   sudo rmdir /config/vkms/my-vkms
 
 Testing With IGT

drivers/gpu/drm/vkms/vkms_configfs.c

@@ -17,6 +17,7 @@ static bool is_configfs_registered;
  * @group: Top level configuration group that represents a VKMS device.
  * Initialized when a new directory is created under "/config/vkms/"
  * @planes_group: Default subgroup of @group at "/config/vkms/planes"
+ * @crtcs_group: Default subgroup of @group at "/config/vkms/crtcs"
  * @lock: Lock used to project concurrent access to the configuration attributes
  * @config: Protected by @lock. Configuration of the VKMS device
  * @enabled: Protected by @lock. The device is created or destroyed when this
@@ -25,6 +26,7 @@ static bool is_configfs_registered;
 struct vkms_configfs_device {
 	struct config_group group;
 	struct config_group planes_group;
+	struct config_group crtcs_group;
 
 	struct mutex lock;
 	struct vkms_config *config;
@@ -45,6 +47,20 @@ struct vkms_configfs_plane {
 	struct vkms_config_plane *config;
 };
 
+/**
+ * struct vkms_configfs_crtc - Configfs representation of a CRTC
+ *
+ * @group: Top level configuration group that represents a CRTC.
+ * Initialized when a new directory is created under "/config/vkms/crtcs"
+ * @dev: The vkms_configfs_device this CRTC belongs to
+ * @config: Configuration of the VKMS CRTC
+ */
+struct vkms_configfs_crtc {
+	struct config_group group;
+	struct vkms_configfs_device *dev;
+	struct vkms_config_crtc *config;
+};
+
 #define device_item_to_vkms_configfs_device(item) \
 	container_of(to_config_group((item)), struct vkms_configfs_device, \
 		     group)
@@ -55,6 +71,71 @@ struct vkms_configfs_plane {
 #define plane_item_to_vkms_configfs_plane(item) \
 	container_of(to_config_group((item)), struct vkms_configfs_plane, group)
 
+#define crtc_item_to_vkms_configfs_crtc(item) \
+	container_of(to_config_group((item)), struct vkms_configfs_crtc, group)
+
+static void crtc_release(struct config_item *item)
+{
+	struct vkms_configfs_crtc *crtc;
+	struct mutex *lock;
+
+	crtc = crtc_item_to_vkms_configfs_crtc(item);
+	lock = &crtc->dev->lock;
+
+	scoped_guard(mutex, lock) {
+		vkms_config_destroy_crtc(crtc->dev->config, crtc->config);
+		kfree(crtc);
+	}
+}
+
+static struct configfs_item_operations crtc_item_operations = {
+	.release	= &crtc_release,
+};
+
+static const struct config_item_type crtc_item_type = {
+	.ct_item_ops	= &crtc_item_operations,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct config_group *make_crtc_group(struct config_group *group,
+					    const char *name)
+{
+	struct vkms_configfs_device *dev;
+	struct vkms_configfs_crtc *crtc;
+
+	dev = child_group_to_vkms_configfs_device(group);
+
+	scoped_guard(mutex, &dev->lock) {
+		if (dev->enabled)
+			return ERR_PTR(-EBUSY);
+
+		crtc = kzalloc(sizeof(*crtc), GFP_KERNEL);
+		if (!crtc)
+			return ERR_PTR(-ENOMEM);
+
+		crtc->dev = dev;
+
+		crtc->config = vkms_config_create_crtc(dev->config);
+		if (IS_ERR(crtc->config)) {
+			kfree(crtc);
+			return ERR_CAST(crtc->config);
+		}
+
+		config_group_init_type_name(&crtc->group, name, &crtc_item_type);
+	}
+
+	return &crtc->group;
+}
+
+static struct configfs_group_operations crtcs_group_operations = {
+	.make_group	= &make_crtc_group,
+};
+
+static const struct config_item_type crtc_group_type = {
+	.ct_group_ops	= &crtcs_group_operations,
+	.ct_owner	= THIS_MODULE,
+};
+
 static ssize_t plane_type_show(struct config_item *item, char *page)
 {
 	struct vkms_configfs_plane *plane;
@@ -262,6 +343,10 @@ static struct config_group *make_device_group(struct config_group *group,
 				    &plane_group_type);
 	configfs_add_default_group(&dev->planes_group, &dev->group);
 
+	config_group_init_type_name(&dev->crtcs_group, "crtcs",
+				    &crtc_group_type);
+	configfs_add_default_group(&dev->crtcs_group, &dev->group);
+
 	return &dev->group;
 }