drm/bridge: panel: Prevent ERR_PTR Dereference

Commit 5ea6b1702781 ("drm/panel: Add prepare_prev_first flag to
drm_panel") introduced an access to the bridge pointer in the
devm_drm_panel_bridge_add_typed() function.

However, due to the unusual ERR_PTR check when getting that pointer, the
pointer access is done even though the pointer might be an error
pointer.

Rework the function for a more traditional design that will return
immediately if it gets an ERR_PTR so that we never access the pointer in
that case.

Fixes: 5ea6b1702781 ("drm/panel: Add prepare_prev_first flag to drm_panel")
Reported-by: kernel test robot <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
Reviewed-by: Laurent Pinchart <[email protected]>
Reviewed-by: Andrzej Hajda <[email protected]>
Signed-off-by: Maxime Ripard <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

1 files changed, 5 insertions, 4 deletions

diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
index 1708098fba6d..e8aae3cdc73d 100644
--- a/drivers/gpu/drm/bridge/panel.c
+++ b/drivers/gpu/drm/bridge/panel.c
@@ -357,15 +357,16 @@ struct drm_bridge *devm_drm_panel_bridge_add_typed(struct device *dev,
 		return ERR_PTR(-ENOMEM);
 
 	bridge = drm_panel_bridge_add_typed(panel, connector_type);
-	if (!IS_ERR(bridge)) {
-		*ptr = bridge;
-		devres_add(dev, ptr);
-	} else {
+	if (IS_ERR(bridge)) {
 		devres_free(ptr);
+		return bridge;
 	}
 
 	bridge->pre_enable_prev_first = panel->prepare_prev_first;
 
+	*ptr = bridge;
+	devres_add(dev, ptr);
+
 	return bridge;
 }
 EXPORT_SYMBOL(devm_drm_panel_bridge_add_typed);