Re: [PATCH v4 5/7] drm/rockchip: cdn-dp: Add multiple bridges to support PHY port selection

[Chaoyi Chen <chaoyi.chen@rock-chips.com>]

On 9/23/2025 9:50 AM, Dmitry Baryshkov wrote:

[...]


>> +	/* One endpoint may correspond to one HPD bridge. */
>> +	for_each_of_graph_port_endpoint(port, dp_ep) {
>> +		/* Try to get "port" node of correspond PHY device */
>> +		struct device_node *phy_ep __free(device_node) =
>> +			of_graph_get_remote_endpoint(dp_ep);
>> +		struct device_node *phy_port __free(device_node) =
>> +			of_get_parent(phy_ep);
>> +
>> +		if (!phy_port) {
>> +			continue;
>> +		}
>> +
>> +		/*
>> +		 * A PHY port may contain two endpoints: USB connector port or CDN-DP port.
>> +		 * Try to find the node of USB connector.
> And then there can be a retimer between PHY and the USB-C connector. Or
> some signal MUX. Or DP-to-HDMI bridge. Please, don't parse DT for other
> devices. Instead you can add drm_aux_bridge to your PHY and let DRM core
> build the bridge chain following OF graph.
>
I think building a bridge chain across multiple drm_aux_hpd_bridge may be difficult. First, drm_dp_hpd_bridge_register() cannot register the bridge immediately; instead, it is deferred until drm_aux_hpd_bridge_probe(). When it is added to the bridge_list, it may not yet be attached, and attempting to attach it at that point is too late.

But, if I only use drm_aux_bridge on the USB-C connector, and use my own custom bridge on the PHY device and managing the alloc and attach bridge process myself, then things would become much easier.

-- 
Best,
Chaoyi