drm/bridge: aux-hpd: separate allocation and registration

Combining allocation and registration is an anti-pattern that should be
avoided. Add two new functions for allocating and registering an dp-hpd
bridge with a proper 'devm' prefix so that it is clear that these are
device managed interfaces.

	devm_drm_dp_hpd_bridge_alloc()
	devm_drm_dp_hpd_bridge_add()

The new interface will be used to fix a use-after-free bug in the
Qualcomm PMIC GLINK driver and may prevent similar issues from being
introduced elsewhere.

The existing drm_dp_hpd_bridge_register() is reimplemented using the
above and left in place for now.
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240217150228.5788-3-johan+linaro@kernel.org

drivers/gpu/drm/bridge/aux-hpd-bridge.c

@@ -30,16 +30,13 @@ static void drm_aux_hpd_bridge_release(struct device *dev)
 	kfree(adev);
 }
 
-static void drm_aux_hpd_bridge_unregister_adev(void *_adev)
+static void drm_aux_hpd_bridge_free_adev(void *_adev)
 {
-	struct auxiliary_device *adev = _adev;
-
-	auxiliary_device_delete(adev);
-	auxiliary_device_uninit(adev);
+	auxiliary_device_uninit(_adev);
 }
 
 /**
- * drm_dp_hpd_bridge_register - Create a simple HPD DisplayPort bridge
+ * devm_drm_dp_hpd_bridge_alloc - allocate a HPD DisplayPort bridge
  * @parent: device instance providing this bridge
  * @np: device node pointer corresponding to this bridge instance
  *
@@ -47,11 +44,9 @@ static void drm_aux_hpd_bridge_unregister_adev(void *_adev)
  * DRM_MODE_CONNECTOR_DisplayPort, which terminates the bridge chain and is
  * able to send the HPD events.
  *
- * Return: device instance that will handle created bridge or an error code
- * encoded into the pointer.
+ * Return: bridge auxiliary device pointer or an error pointer
  */
-struct device *drm_dp_hpd_bridge_register(struct device *parent,
-					  struct device_node *np)
+struct auxiliary_device *devm_drm_dp_hpd_bridge_alloc(struct device *parent, struct device_node *np)
 {
 	struct auxiliary_device *adev;
 	int ret;
@@ -82,13 +77,55 @@ struct device *drm_dp_hpd_bridge_register(struct device *parent,
 		return ERR_PTR(ret);
 	}
 
-	ret = auxiliary_device_add(adev);
-	if (ret) {
-		auxiliary_device_uninit(adev);
+	ret = devm_add_action_or_reset(parent, drm_aux_hpd_bridge_free_adev, adev);
+	if (ret)
 		return ERR_PTR(ret);
-	}
 
-	ret = devm_add_action_or_reset(parent, drm_aux_hpd_bridge_unregister_adev, adev);
+	return adev;
+}
+EXPORT_SYMBOL_GPL(devm_drm_dp_hpd_bridge_alloc);
+
+static void drm_aux_hpd_bridge_del_adev(void *_adev)
+{
+	auxiliary_device_delete(_adev);
+}
+
+/**
+ * devm_drm_dp_hpd_bridge_add - register a HDP DisplayPort bridge
+ * @dev: struct device to tie registration lifetime to
+ * @adev: bridge auxiliary device to be registered
+ *
+ * Returns: zero on success or a negative errno
+ */
+int devm_drm_dp_hpd_bridge_add(struct device *dev, struct auxiliary_device *adev)
+{
+	int ret;
+
+	ret = auxiliary_device_add(adev);
+	if (ret)
+		return ret;
+
+	return devm_add_action_or_reset(dev, drm_aux_hpd_bridge_del_adev, adev);
+}
+EXPORT_SYMBOL_GPL(devm_drm_dp_hpd_bridge_add);
+
+/**
+ * drm_dp_hpd_bridge_register - allocate and register a HDP DisplayPort bridge
+ * @parent: device instance providing this bridge
+ * @np: device node pointer corresponding to this bridge instance
+ *
+ * Return: device instance that will handle created bridge or an error pointer
+ */
+struct device *drm_dp_hpd_bridge_register(struct device *parent, struct device_node *np)
+{
+	struct auxiliary_device *adev;
+	int ret;
+
+	adev = devm_drm_dp_hpd_bridge_alloc(parent, np);
+	if (IS_ERR(adev))
+		return ERR_CAST(adev);
+
+	ret = devm_drm_dp_hpd_bridge_add(parent, adev);
 	if (ret)
 		return ERR_PTR(ret);
 

include/drm/bridge/aux-bridge.h

@@ -9,6 +9,8 @@
 
 #include <drm/drm_connector.h>
 
+struct auxiliary_device;
+
 #if IS_ENABLED(CONFIG_DRM_AUX_BRIDGE)
 int drm_aux_bridge_register(struct device *parent);
 #else
@@ -19,10 +21,23 @@ static inline int drm_aux_bridge_register(struct device *parent)
 #endif
 
 #if IS_ENABLED(CONFIG_DRM_AUX_HPD_BRIDGE)
+struct auxiliary_device *devm_drm_dp_hpd_bridge_alloc(struct device *parent, struct device_node *np);
+int devm_drm_dp_hpd_bridge_add(struct device *dev, struct auxiliary_device *adev);
 struct device *drm_dp_hpd_bridge_register(struct device *parent,
 					  struct device_node *np);
 void drm_aux_hpd_bridge_notify(struct device *dev, enum drm_connector_status status);
 #else
+static inline struct auxiliary_device *devm_drm_dp_hpd_bridge_alloc(struct device *parent,
+								    struct device_node *np)
+{
+	return NULL;
+}
+
+static inline int devm_drm_dp_hpd_bridge_add(struct auxiliary_device *adev)
+{
+	return 0;
+}
+
 static inline struct device *drm_dp_hpd_bridge_register(struct device *parent,
 							struct device_node *np)
 {