[PATCH v2 1/4] drm/debugfs: Add support for dynamic debugfs initialization

[Lyude Paul]

Currently all debugfs related initialization for the DRM core happens in
drm_debugfs_init(), which is called when registering the minor device.
While this works fine for features such as atomic modesetting and GEM,
this doesn't work at all for resources like DP MST topology managers
which can potentially be created both before and after the minor
device has been registered.

So, in order to add driver-wide debugfs files for MST we'll need to be
able to handle debugfs initialization for such resources. We do so by
introducing drm_debugfs_callback_register() and
drm_debugfs_callback_unregister(). These functions allow driver-agnostic
parts of DRM to add additional debugfs initialization callbacks at any
point during a DRM driver's lifetime.

Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Daniel Stone <daniel@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_debugfs.c  | 173 +++++++++++++++++++++++++++++++--
 drivers/gpu/drm/drm_drv.c      |   3 +
 drivers/gpu/drm/drm_internal.h |   5 +
 include/drm/drm_debugfs.h      |  27 +++++
 include/drm/drm_file.h         |   4 +
 5 files changed, 203 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
index 6f28fe58f169..a53a454b167f 100644
--- a/drivers/gpu/drm/drm_debugfs.c
+++ b/drivers/gpu/drm/drm_debugfs.c
@@ -39,6 +39,13 @@
 
 #if defined(CONFIG_DEBUG_FS)
 
+struct drm_debugfs_callback {
+	void (*init)(void *data);
+	void (*cleanup_cb)(void *data);
+	void *data;
+	struct list_head list;
+};
+
 /***************************************************
  * Initialization, etc.
  **************************************************/
@@ -67,6 +74,113 @@ static const struct file_operations drm_debugfs_fops = {
 	.release = single_release,
 };
 
+/**
+ * drm_debugfs_register_callback - Register a callback for initializing
+ *                                 dynamic driver-agnostic debugfs files
+ * @minor: device minor number
+ * @init: The callback to invoke to perform the debugfs initialization
+ * @cleanup_cb: The callback to invoke to cleanup any resources for the
+ * callback
+ * @data: Data to pass to @init and @cleanup_cb
+ * @out: Where to store the pointer to the callback struct
+ *
+ * Register an initialization callback with debugfs. This callback can be used
+ * to creating debugfs nodes for DRM resources that might get created before
+ * the debugfs node for @minor has been created.
+ *
+ * When a callback is registered with this function before the debugfs root
+ * has been created, the callback's execution will be delayed until all other
+ * debugfs nodes (including those owned by the DRM device's driver) have been
+ * instantiated. If a callback is registered with this function after the
+ * debugfs root has been created, @init and @cleanup_cb will be executed
+ * immediately without creating a &struct drm_debugfs_callback.
+ *
+ * In the event that debugfs creation for the device fails; all registered
+ * debugfs callbacks will have their @cleanup_cb callbacks invoked without
+ * having their @init callbacks invoked. This is to ensure that no resources
+ * are leaked during initialization of debugfs, even if the initialization
+ * process fails. Likewise; any callbacks that are registered after DRM has
+ * failed to initialize it's debugfs files will have their @cleanup_cb
+ * callbacks invoked immediately and all of their respective resources
+ * destroyed.
+ *
+ * Implementations of @cleanup_cb should clean up all resources for the
+ * callback, with the exception of freeing the memory for @out. Freeing @out
+ * will be handled by the DRM core automatically.
+ *
+ * Users of this function should take care to add a symmetric call to
+ * @drm_debugfs_unregister_callback to handle destroying a registered callback
+ * in case the resources for the user of this function are destroyed before
+ * debugfs root is initialized.
+ *
+ */
+int
+drm_debugfs_register_callback(struct drm_minor *minor,
+			      void (*init)(void *),
+			      void (*cleanup_cb)(void *),
+			      void *data, struct drm_debugfs_callback **out)
+{
+	int ret = 0;
+
+	mutex_lock(&minor->debugfs_callback_lock);
+	if (minor->debugfs_callbacks_done) {
+		/* debugfs is already setup, so just handle the callback
+		 * immediately
+		 */
+		if (minor->debugfs_root)
+			(*init)(data);
+		(*cleanup_cb)(data);
+		goto out_unlock;
+	}
+
+	*out = kzalloc(sizeof(**out), GFP_KERNEL);
+	if (!*out) {
+		ret = -ENOMEM;
+		goto out_unlock;
+	}
+
+	(*out)->init = init;
+	(*out)->cleanup_cb = cleanup_cb;
+	(*out)->data = data;
+	list_add(&(*out)->list, &minor->debugfs_callback_list);
+
+out_unlock:
+	mutex_unlock(&minor->debugfs_callback_lock);
+	return ret;
+}
+EXPORT_SYMBOL(drm_debugfs_register_callback);
+
+/**
+ * drm_debugfs_unregister_callback - Unregister and release the resources
+ *                                   associated with a debugfs init callback
+ * @minor: device minor number
+ * @cb: A pointer to the &struct drm_debugfs_callback struct returned by
+ * drm_debugfs_register_callback(). May be NULL
+ *
+ * Unregisters a &struct drm_debugfs_callback struct with debugfs and destroys
+ * all of it's associated resources. This includes a call to the callback's
+ * @cleanup_cb implementation.
+ *
+ * Once the debugfs root is initialized or has failed initialization, all
+ * registered callbacks are automatically destroyed. If this function is
+ * called after that point; it will automatically be a no-op.
+ */
+void
+drm_debugfs_unregister_callback(struct drm_minor *minor,
+				struct drm_debugfs_callback *cb)
+{
+	mutex_lock(&minor->debugfs_callback_lock);
+	/* We don't have to do anything if we've already completed any
+	 * registered callbacks, as they will have already been destroyed
+	 */
+	if (!minor->debugfs_callbacks_done) {
+		cb->cleanup_cb(cb->data);
+		list_del(&cb->list);
+		kfree(cb);
+	}
+	mutex_unlock(&minor->debugfs_callback_lock);
+}
+EXPORT_SYMBOL(drm_debugfs_unregister_callback);
 
 /**
  * drm_debugfs_create_files - Initialize a given set of debugfs files for DRM
@@ -126,12 +240,24 @@ int drm_debugfs_create_files(const struct drm_info_list *files, int count,
 }
 EXPORT_SYMBOL(drm_debugfs_create_files);
 
+int drm_debugfs_alloc(struct drm_minor *minor)
+{
+	INIT_LIST_HEAD(&minor->debugfs_callback_list);
+	mutex_init(&minor->debugfs_callback_lock);
+	return 0;
+}
+
 int drm_debugfs_init(struct drm_minor *minor, int minor_id,
 		     struct dentry *root)
 {
 	struct drm_device *dev = minor->dev;
+	struct drm_debugfs_callback *pos, *tmp;
 	char name[64];
-	int ret;
+	int ret = 0;
+
+	/* Don't allow any more callbacks to be registered while we setup */
+	mutex_lock(&minor->debugfs_callback_lock);
+	minor->debugfs_callbacks_done = true;
 
 	INIT_LIST_HEAD(&minor->debugfs_list);
 	mutex_init(&minor->debugfs_lock);
@@ -139,7 +265,8 @@ int drm_debugfs_init(struct drm_minor *minor, int minor_id,
 	minor->debugfs_root = debugfs_create_dir(name, root);
 	if (!minor->debugfs_root) {
 		DRM_ERROR("Cannot create /sys/kernel/debug/dri/%s\n", name);
-		return -1;
+		ret = -1;
+		goto out_unlock;
 	}
 
 	ret = drm_debugfs_create_files(drm_debugfs_list, DRM_DEBUGFS_ENTRIES,
@@ -148,14 +275,14 @@ int drm_debugfs_init(struct drm_minor *minor, int minor_id,
 		debugfs_remove(minor->debugfs_root);
 		minor->debugfs_root = NULL;
 		DRM_ERROR("Failed to create core drm debugfs files\n");
-		return ret;
+		goto out_unlock;
 	}
 
 	if (drm_core_check_feature(dev, DRIVER_ATOMIC)) {
 		ret = drm_atomic_debugfs_init(minor);
 		if (ret) {
 			DRM_ERROR("Failed to create atomic debugfs files\n");
-			return ret;
+			goto out_unlock;
 		}
 	}
 
@@ -163,13 +290,13 @@ int drm_debugfs_init(struct drm_minor *minor, int minor_id,
 		ret = drm_framebuffer_debugfs_init(minor);
 		if (ret) {
 			DRM_ERROR("Failed to create framebuffer debugfs file\n");
-			return ret;
+			goto out_unlock;
 		}
 
 		ret = drm_client_debugfs_init(minor);
 		if (ret) {
 			DRM_ERROR("Failed to create client debugfs file\n");
-			return ret;
+			goto out_unlock;
 		}
 	}
 
@@ -178,10 +305,23 @@ int drm_debugfs_init(struct drm_minor *minor, int minor_id,
 		if (ret) {
 			DRM_ERROR("DRM: Driver failed to initialize "
 				  "/sys/kernel/debug/dri.\n");
-			return ret;
+			goto out_unlock;
 		}
 	}
-	return 0;
+
+out_unlock:
+	/* Execute any delayed callbacks if we succeeded, or just clean them
+	 * up without running them if we failed
+	 */
+	list_for_each_entry_safe(pos, tmp, &minor->debugfs_callback_list,
+				 list) {
+		if (!ret)
+			pos->init(pos->data);
+		pos->cleanup_cb(pos->data);
+		kfree(pos);
+	}
+	mutex_unlock(&minor->debugfs_callback_lock);
+	return ret;
 }
 
 
@@ -223,14 +363,29 @@ static void drm_debugfs_remove_all_files(struct drm_minor *minor)
 
 int drm_debugfs_cleanup(struct drm_minor *minor)
 {
+	struct drm_debugfs_callback *pos, *tmp;
+
+	mutex_lock(&minor->debugfs_callback_lock);
+	if (!minor->debugfs_callbacks_done) {
+		list_for_each_entry_safe(pos, tmp,
+					 &minor->debugfs_callback_list,
+					 list) {
+			pos->cleanup_cb(pos->data);
+			kfree(pos);
+		}
+	}
+	minor->debugfs_callbacks_done = true;
+
 	if (!minor->debugfs_root)
-		return 0;
+		goto out;
 
 	drm_debugfs_remove_all_files(minor);
 
 	debugfs_remove_recursive(minor->debugfs_root);
 	minor->debugfs_root = NULL;
 
+out:
+	mutex_unlock(&minor->debugfs_callback_lock);
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index ea4941da9b27..7041b3137229 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -118,6 +118,9 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
 
 	minor->type = type;
 	minor->dev = dev;
+	r = drm_debugfs_alloc(minor);
+	if (r)
+		goto err_free;
 
 	idr_preload(GFP_KERNEL);
 	spin_lock_irqsave(&drm_minor_lock, flags);
diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
index 40179c5fc6b8..d6394246967d 100644
--- a/drivers/gpu/drm/drm_internal.h
+++ b/drivers/gpu/drm/drm_internal.h
@@ -118,6 +118,7 @@ void drm_gem_print_info(struct drm_printer *p, unsigned int indent,
 
 /* drm_debugfs.c drm_debugfs_crc.c */
 #if defined(CONFIG_DEBUG_FS)
+int drm_debugfs_alloc(struct drm_minor *minor);
 int drm_debugfs_init(struct drm_minor *minor, int minor_id,
 		     struct dentry *root);
 int drm_debugfs_cleanup(struct drm_minor *minor);
@@ -127,6 +128,10 @@ int drm_debugfs_crtc_add(struct drm_crtc *crtc);
 void drm_debugfs_crtc_remove(struct drm_crtc *crtc);
 int drm_debugfs_crtc_crc_add(struct drm_crtc *crtc);
 #else
+static inline int drm_debugfs_alloc(struct drm_minor *minor)
+{
+	return 0;
+}
 static inline int drm_debugfs_init(struct drm_minor *minor, int minor_id,
 				   struct dentry *root)
 {
diff --git a/include/drm/drm_debugfs.h b/include/drm/drm_debugfs.h
index ac0f75df1ac9..6ac45d96fcd1 100644
--- a/include/drm/drm_debugfs.h
+++ b/include/drm/drm_debugfs.h
@@ -77,12 +77,23 @@ struct drm_info_node {
 	struct dentry *dent;
 };
 
+struct drm_debugfs_callback;
+
 #if defined(CONFIG_DEBUG_FS)
 int drm_debugfs_create_files(const struct drm_info_list *files,
 			     int count, struct dentry *root,
 			     struct drm_minor *minor);
 int drm_debugfs_remove_files(const struct drm_info_list *files,
 			     int count, struct drm_minor *minor);
+
+int drm_debugfs_register_callback(struct drm_minor *minor,
+				  void (*init)(void *),
+				  void (*cleanup_cb)(void *),
+				  void *data,
+				  struct drm_debugfs_callback **out);
+void drm_debugfs_unregister_callback(struct drm_minor *minor,
+				     struct drm_debugfs_callback *cb);
+
 #else
 static inline int drm_debugfs_create_files(const struct drm_info_list *files,
 					   int count, struct dentry *root,
@@ -96,6 +107,22 @@ static inline int drm_debugfs_remove_files(const struct drm_info_list *files,
 {
 	return 0;
 }
+
+static inline int
+drm_debugfs_register_callback(struct drm_minor *minor,
+			      void (*init)(void *),
+			      void (*cleanup_cb)(void *),
+			      void *data,
+			      struct drm_debugfs_callback **out)
+{
+	return 0;
+}
+
+static inline void
+drm_debugfs_unregister_callback(struct drm_minor *minor,
+				struct drm_debugfs_callback *cb)
+{
+}
 #endif
 
 #endif /* _DRM_DEBUGFS_H_ */
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 26485acc51d7..180052b51712 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -74,6 +74,10 @@ struct drm_minor {
 
 	struct dentry *debugfs_root;
 
+	bool debugfs_callbacks_done;
+	struct list_head debugfs_callback_list;
+	struct mutex debugfs_callback_lock;
+
 	struct list_head debugfs_list;
 	struct mutex debugfs_lock; /* Protects debugfs_list. */
 };
-- 
2.17.1