drm/msm/dp: fix panel bridge attachment

In commit 8a3b4c17 ("drm/msm/dp: employ bridge mechanism for display
enable and disable") the DP driver received a drm_bridge instance, which
is always attached to the encoder as a root bridge. However it conflicts
with the panel_bridge support for eDP panels. The panel bridge attaches
to the encoder before the "dp" bridge (DP driver's drm_bridge instance
created in msm_dp_bridge_init()) has a chance to do so. Change
panel bridge attachment to come after the "dp" bridge attachment (and to
use it as a previous bridge).

Fixes: 8a3b4c17 ("drm/msm/dp: employ bridge mechanism for display enable and disable")
Cc: Kuogee Hsieh <quic_khsieh@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20220211224006.1797846-2-dmitry.baryshkov@linaro.org
[db: fixed commit message according to Stephen's suggestions]
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/dp/dp_drm.c

@@ -169,16 +169,6 @@ struct drm_connector *dp_drm_connector_init(struct msm_dp *dp_display)
 
 	drm_connector_attach_encoder(connector, dp_display->encoder);
 
-	if (dp_display->panel_bridge) {
-		ret = drm_bridge_attach(dp_display->encoder,
-					dp_display->panel_bridge, NULL,
-					DRM_BRIDGE_ATTACH_NO_CONNECTOR);
-		if (ret < 0) {
-			DRM_ERROR("failed to attach panel bridge: %d\n", ret);
-			return ERR_PTR(ret);
-		}
-	}
-
 	return connector;
 }
 
@@ -246,5 +236,16 @@ struct drm_bridge *msm_dp_bridge_init(struct msm_dp *dp_display, struct drm_devi
 		return ERR_PTR(rc);
 	}
 
+	if (dp_display->panel_bridge) {
+		rc = drm_bridge_attach(dp_display->encoder,
+					dp_display->panel_bridge, bridge,
+					DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+		if (rc < 0) {
+			DRM_ERROR("failed to attach panel bridge: %d\n", rc);
+			drm_bridge_remove(bridge);
+			return ERR_PTR(rc);
+		}
+	}
+
 	return bridge;
 }