[RFC v4 23/25] drm: Add DRM device registered notifier

[Noralf Trønnes]

Add a notifier that fires when a new DRM device is registered.
This can be used by the bootsplash client to connect to all devices.

Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
---
 drivers/gpu/drm/drm_drv.c | 32 ++++++++++++++++++++++++++++++++
 include/drm/drm_drv.h     |  4 ++++
 2 files changed, 36 insertions(+)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 6f21bafb29be..e42ce320ad07 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -31,6 +31,7 @@
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/mount.h>
+#include <linux/notifier.h>
 #include <linux/slab.h>
 #include <linux/srcu.h>
 
@@ -79,6 +80,8 @@ static struct dentry *drm_debugfs_root;
 
 DEFINE_STATIC_SRCU(drm_unplug_srcu);
 
+static BLOCKING_NOTIFIER_HEAD(drm_dev_notifier);
+
 /*
  * DRM Minors
  * A DRM device can provide several char-dev interfaces on the DRM-Major. Each
@@ -837,6 +840,8 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags)
 		 dev->dev ? dev_name(dev->dev) : "virtual device",
 		 dev->primary->index);
 
+	blocking_notifier_call_chain(&drm_dev_notifier, 0, dev);
+
 	goto out_unlock;
 
 err_minors:
@@ -894,6 +899,33 @@ void drm_dev_unregister(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_dev_unregister);
 
+/**
+ * drm_dev_register_notifier - Register a notifier for new DRM devices
+ * @nb: Notifier block
+ *
+ * Register a notifier that fires when a new &drm_device is registered.
+ *
+ * Note:
+ * Users of this function has to be linked into drm.ko. This is done to make
+ * life simple avoiding tricky race situations.
+ */
+void drm_dev_register_notifier(struct notifier_block *nb)
+{
+	/* Currently this can't fail, but catch it in case this changes */
+	WARN_ON(blocking_notifier_chain_register(&drm_dev_notifier, nb));
+}
+
+/**
+ * drm_dev_unregister_notifier - Unregister DRM device notifier
+ * @nb: Notifier block
+ *
+ * This is a no-op if the notifier isn't registered.
+ */
+void drm_dev_unregister_notifier(struct notifier_block *nb)
+{
+	blocking_notifier_chain_unregister(&drm_dev_notifier, nb);
+}
+
 /**
  * drm_dev_set_unique - Set the unique name of a DRM device
  * @dev: device of which to set the unique name
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index 13356e6fd40c..5e6c6ed0d59d 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -40,6 +40,7 @@ struct drm_minor;
 struct dma_buf_attachment;
 struct drm_display_mode;
 struct drm_mode_create_dumb;
+struct notifier_block;
 struct drm_printer;
 
 /* driver capabilities and requirements mask */
@@ -641,6 +642,9 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
 int drm_dev_register(struct drm_device *dev, unsigned long flags);
 void drm_dev_unregister(struct drm_device *dev);
 
+void drm_dev_register_notifier(struct notifier_block *nb);
+void drm_dev_unregister_notifier(struct notifier_block *nb);
+
 void drm_dev_get(struct drm_device *dev);
 void drm_dev_put(struct drm_device *dev);
 void drm_dev_unref(struct drm_device *dev);
-- 
2.15.1