linux-kernel - [PATCH] drm/bridge: panel: Fix device link for DRM_BRIDGE_ATTACH_NO

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Date:   Mon, 18 Sep 2023 17:00:43 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     andrzej.hajda@...el.com
Cc:     neil.armstrong@...aro.org, rfoss@...nel.org,
        Laurent.pinchart@...asonboard.com, jonas@...boo.se,
        jernej.skrabec@...il.com, airlied@...il.com, daniel@...ll.ch,
        ulf.hansson@...aro.org, victor.liu@....com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, ehristev@...labora.com, wenst@...omium.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Subject: [PATCH] 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@...labora.com>
---
 drivers/gpu/drm/bridge/panel.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
index e00d2e94c751..8c507dfd589e 100644
--- 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 +75,14 @@ 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");
+		return -ENODEV;
+	}
+
 	drm_connector_helper_add(connector,
 				 &panel_bridge_connector_helper_funcs);
 
-- 
2.42.0