Re: [PATCH v2 06/10] drm/bridge: dw-hdmi: warn on unsupported attach combination

[Damon Ding]

On 3/31/2026 3:25 AM, Luca Ceresoli wrote:
> 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@xxxxxxx>
> Tested-by: Martyn Welch <martyn.welch@xxxxxxxxxxxxx>
> Tested-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx> # TQMa8MPxL/MBa8MPxL
> Signed-off-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>
> ---
> 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);

Tested-by: Damon Ding <damon.ding@xxxxxxxxxxxxxx> (on rk3399)

Best regards,
Damon