[PATCH] drm/bridge: introduce bridge detaching mechanism

[Andrea Merello <andrea.merello@xxxxxxxxx>]

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().

Suggested-by: Daniel Vetter <daniel@xxxxxxxx>
Suggested-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
Signed-off-by: Andrea Merello <andrea.merello@xxxxxxxxx>
Cc: Archit Taneja <architt@xxxxxxxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx>

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 2555430..c4ace90 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -125,6 +125,39 @@ 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 one of our encoder/bridge to the given
+ * bridge.
+ *
+ * Note that tearing down links between the bridge and our encoder/bridge
+ * objects needs to be handled by the kms driver itself
+ *
+ * RETURNS:
+ * Zero on success, error code on failure
+ */
+int drm_bridge_detach(struct drm_bridge *bridge)
+{
+	int ret;
+
+	if (!bridge || !bridge->dev)
+		return -EINVAL;
+
+	if (bridge->funcs->detach) {
+		ret = bridge->funcs->detach(bridge);
+		if (ret)
+			return ret;
+	}
+
+	bridge->dev = NULL;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_bridge_detach);
+
+/**
  * DOC: bridge callbacks
  *
  * The &drm_bridge_funcs ops are populated by the bridge driver. The DRM
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index b618b50..eef4db8 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1766,6 +1766,7 @@ struct drm_plane {
  */
 struct drm_bridge_funcs {
 	int (*attach)(struct drm_bridge *bridge);
+	int (*detach)(struct drm_bridge *bridge);

 	/**
 	 * @mode_fixup:
@@ -3196,6 +3197,7 @@ 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 int drm_bridge_detach(struct drm_bridge *bridge);

 bool drm_bridge_mode_fixup(struct drm_bridge *bridge,
 			const struct drm_display_mode *mode,
--
2.7.4
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