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From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
To:     andrzej.hajda@intel.com
Cc:     neil.armstrong@linaro.org, rfoss@kernel.org,
        Laurent.pinchart@ideasonboard.com, jonas@kwiboo.se,
        jernej.skrabec@gmail.com, airlied@gmail.com, daniel@ffwll.ch,
        ulf.hansson@linaro.org, victor.liu@nxp.com,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        kernel@collabora.com, ehristev@collabora.com, wenst@chromium.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
Subject: [PATCH] drm/bridge: panel: Fix device link for DRM_BRIDGE_ATTACH_NO_CONNECTOR
Date:   Mon, 18 Sep 2023 17:00:43 +0200
Message-ID: <20230918150043.403250-1-angelogioacchino.delregno@collabora.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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>
---
 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