drm/bridge: panel: Fix device link for DRM_BRIDGE_ATTACH_NO_CONNECTOR

When external bridges are attached with DRM_BRIDGE_ATTACH_NO_CONNECTOR,
the panel bridge may also get the same flag, but in the .attach()
callback for the panel bridge a device link is added only when this
flag is not present; To make things worse, the .detach() callback
tries to delete the device link unconditionally and without checking
if it was created in the first place, crashing the kernel with a NULL
pointer kernel panic upon calling panel_bridge_detach().

Fix that by moving the device_link_add() call before checking if the
DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is present.

Fixes: 199cf07ebd2b ("drm/bridge: panel: Add a device link between drm device and panel device")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Liu Ying <victor.liu@nxp.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230920082727.57729-1-angelogioacchino.delregno@collabora.com

diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
index e00d2e9..e48823a 100644 (file)
--- a/drivers/gpu/drm/bridge/panel.c
+++ b/drivers/gpu/drm/bridge/panel.c
@@ -67,14 +67,6 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
        struct drm_device *drm_dev = bridge->dev;
        int ret;
 
-       if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
-               return 0;
-
-       if (!bridge->encoder) {
-               DRM_ERROR("Missing encoder\n");
-               return -ENODEV;
-       }
-
        panel_bridge->link = device_link_add(drm_dev->dev, panel->dev,
                                             DL_FLAG_STATELESS);
        if (!panel_bridge->link) {
@@ -83,6 +75,15 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
                return -EINVAL;
        }
 
+       if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
+               return 0;
+
+       if (!bridge->encoder) {
+               DRM_ERROR("Missing encoder\n");
+               device_link_del(panel_bridge->link);
+               return -ENODEV;
+       }
+
        drm_connector_helper_add(connector,
                                 &panel_bridge_connector_helper_funcs);