Re: [PATCH v1 2/4] drm/bridge: dw-hdmi: Allow &dw_hdmi_plat_data.output_port = 0 without DRM_BRIDGE_ATTACH_NO_CONNECTOR

[Luca Ceresoli]

Hello Damon,

On Fri Apr 3, 2026 at 9:00 AM CEST, Damon Ding wrote:
> In the previous commit, Luca split the dw-hdmi attach process into two
> cases:
>
>  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
>
> For Rockchip, many older platforms (RK3288, RK3399, etc.) only support
> case A by default. They can support DRM_BRIDGE_ATTACH_NO_CONNECTOR flag
> after adapting to the bridge connector helper. Relax this constraint in
> preparation for Rockchip dw-hdmi bridge-connector adaptation.
>
> Link: https://lore.kernel.org/all/20260402-drm-lcdif-dbanc-v3-6-27cd247a0847@xxxxxxxxxxx/
> Signed-off-by: Damon Ding <damon.ding@xxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> index dd50dda3a4f5..20b2f9e145b0 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -2912,9 +2912,8 @@ 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) && !hdmi->plat_data->output_port)
> +		return 0;
>
>  	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
>  		struct device_node *remote __free(device_node) =

My understanding is that a hdmi-connector node is required in DT when using
drm_bridge_connector and DRM_BRIDGE_ATTACH_NO_CONNECTOR. Among others, it
is necessary to expose the correct connector type instead of defaulting to
DRM_MODE_CONNECTOR_HDMIA.

@Dmitry, others, can you confirm or deny the above?

If I'm correct, then the right way to support
DRM_BRIDGE_ATTACH_NO_CONNECTOR here is adding an hdmi-connector node in DT,
perhaps reusing the device tree overlay I proposed in [0].

[0] https://lore.kernel.org/lkml/20260407-drm-lcdif-dbanc-v4-8-247a16e61ef9@xxxxxxxxxxx/

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com