drm/bridge: introduce bridge detaching mechanism

Up to now, once a bridge has been attached to a DRM device, it cannot
be undone.

In particular you couldn't rmmod/insmod a DRM driver that uses a bridge,
because the bridge would remain bound to the first (dead) driver instance.

This patch fixes this by introducing drm_encoder_detach() and a ->detach
callback in drm_bridge_funcs for the bridge to be notified about detaches.

It's DRM/KMS driver responsibility to call drm_encoder_detach().

While adding the bridge detach callback, with its kerneldoc, I also added
kerneldoc for attach callback.

Few other kerneldocs fixes around there are included.
Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Suggested-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1472115874-6219-1-git-send-email-andrea.merello@gmail.com

drivers/gpu/drm/drm_bridge.c

@@ -98,11 +98,11 @@ EXPORT_SYMBOL(drm_bridge_remove);
  * @dev: DRM device
  * @bridge: bridge control structure
  *
- * called by a kms driver to link one of our encoder/bridge to the given
+ * Called by a kms driver to link one of our encoder/bridge to the given
  * bridge.
  *
  * Note that setting up links between the bridge and our encoder/bridge
- * objects needs to be handled by the kms driver itself
+ * objects needs to be handled by the kms driver itself.
  *
  * RETURNS:
  * Zero on success, error code on failure
@@ -124,6 +124,31 @@ int drm_bridge_attach(struct drm_device *dev, struct drm_bridge *bridge)
 }
 EXPORT_SYMBOL(drm_bridge_attach);
 
+/**
+ * drm_bridge_detach - deassociate given bridge from its DRM device
+ *
+ * @bridge: bridge control structure
+ *
+ * Called by a kms driver to unlink the given bridge from its DRM device.
+ *
+ * Note that tearing down links between the bridge and our encoder/bridge
+ * objects needs to be handled by the kms driver itself.
+ */
+void drm_bridge_detach(struct drm_bridge *bridge)
+{
+	if (WARN_ON(!bridge))
+		return;
+
+	if (WARN_ON(!bridge->dev))
+		return;
+
+	if (bridge->funcs->detach)
+		bridge->funcs->detach(bridge);
+
+	bridge->dev = NULL;
+}
+EXPORT_SYMBOL(drm_bridge_detach);
+
 /**
  * DOC: bridge callbacks
  *

include/drm/drm_crtc.h

@@ -1118,11 +1118,32 @@ struct drm_plane {
 
 /**
  * struct drm_bridge_funcs - drm_bridge control functions
- * @attach: Called during drm_bridge_attach
  */
 struct drm_bridge_funcs {
+	/**
+	 * @attach:
+	 *
+	 * This callback is invoked whenever our bridge is being attached to a
+	 * &drm_encoder.
+	 *
+	 * The attach callback is optional.
+	 *
+	 * RETURNS:
+	 *
+	 * Zero on success, error code on failure.
+	 */
 	int (*attach)(struct drm_bridge *bridge);
 
+	/**
+	 * @detach:
+	 *
+	 * This callback is invoked whenever our bridge is being detached from a
+	 * &drm_encoder.
+	 *
+	 * The detach callback is optional.
+	 */
+	void (*detach)(struct drm_bridge *bridge);
+
 	/**
 	 * @mode_fixup:
 	 *
@@ -1137,6 +1158,8 @@ struct drm_bridge_funcs {
 	 * this function passes all other callbacks must succeed for this
 	 * configuration.
 	 *
+	 * The mode_fixup callback is optional.
+	 *
 	 * NOTE:
 	 *
 	 * This function is called in the check phase of atomic modesets, which
@@ -2426,6 +2449,7 @@ extern int drm_bridge_add(struct drm_bridge *bridge);
 extern void drm_bridge_remove(struct drm_bridge *bridge);
 extern struct drm_bridge *of_drm_find_bridge(struct device_node *np);
 extern int drm_bridge_attach(struct drm_device *dev, struct drm_bridge *bridge);
+extern void drm_bridge_detach(struct drm_bridge *bridge);
 
 bool drm_bridge_mode_fixup(struct drm_bridge *bridge,
 			const struct drm_display_mode *mode,