[PATCH v4 06/11] drm/bridge: dw-hdmi: warn on unsupported attach combination

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

dw-hdmi can operate in two different modes, depending on the platform data
as set by the driver:

 A. hdmi->plat_data->output_port = 0:
    the HDMI output (port@1) in device tree is not used

 B. hdmi->plat_data->output_port = 1:
    the HDMI output (port@1) is parsed to find the next bridge

Only case B is supported when the DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is
passed to the attach callback. Emit a warning when this is violated. Also
return -EINVAL which would be returned by drm_bridge_attach() right after
anyway.

Reviewed-by: Liu Ying <victor.liu@nxp.com>
Tested-by: Martyn Welch <martyn.welch@collabora.com>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com> # TQMa8MPxL/MBa8MPxL
Tested-by: Damon Ding <damon.ding@rock-chips.com> # rk3399
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
Note: Returning when the warning triggers does not change the functional
behaviour of this function. It is not strictly necessary in this patch but
it will have to be done anyway in the following patch.
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 0296e110ce65..ab1a6a8783cd 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2910,6 +2910,10 @@ static int dw_hdmi_bridge_attach(struct drm_bridge *bridge,
 {
 	struct dw_hdmi *hdmi = bridge->driver_private;
 
+	/* DRM_BRIDGE_ATTACH_NO_CONNECTOR requires a remote-endpoint to the next bridge */
+	if (WARN_ON((flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) && !hdmi->plat_data->output_port))
+		return -EINVAL;
+
 	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
 		return drm_bridge_attach(encoder, hdmi->bridge.next_bridge,
 					 bridge, flags);

-- 
2.53.0