Re: [PATCH v5 6/8] drm/rockchip: cdn-dp: Add multiple bridges to support PHY port selection

Chaoyi Chen
2025-10-13T02:45:09Z

On 10/13/2025 10:11 AM, Dmitry Baryshkov wrote:

> On Mon, Oct 13, 2025 at 09:26:06AM +0800, Chaoyi Chen wrote:
>> On 10/12/2025 2:52 AM, Dmitry Baryshkov wrote:
>>
>>> On Sat, Oct 11, 2025 at 11:32:31AM +0800, Chaoyi Chen wrote:
>>>> From: Chaoyi Chen <chaoyi.chen@rock-chips.com>
>>>>
>>>> The RK3399 has two USB/DP combo PHY and one CDN-DP controller. And
>>>> the CDN-DP can be switched to output to one of the PHYs. If both ports
>>>> are plugged into DP, DP will select the first port for output.
>>>>
>>>> This patch adds support for multiple bridges, enabling users to flexibly
>>>> select the output port. For each PHY port, a separate encoder and bridge
>>>> are registered.
>>>>
>>>> The change is based on the DRM AUX HPD bridge, rather than the
>>>> extcon approach. This requires the DT to correctly describe the
>>>> connections between the first bridge in bridge chain and DP
>>>> controller. For example, the bridge chain may be like this:
>>>>
>>>> PHY aux birdge -> fsa4480 analog audio switch bridge ->
>>>> onnn,nb7vpq904m USB reminder bridge -> USB-C controller AUX HPD bridge
>>>>
>>>> In this case, the connection relationships among the PHY aux bridge
>>>> and the DP contorller need to be described in DT.
>>>>
>>>> In addition, the cdn_dp_parse_hpd_bridge_dt() will parses it and
>>>> determines whether to register one or two bridges.
>>>>
>>>> Since there is only one DP controller, only one of the PHY ports can
>>>> output at a time. The key is how to switch between different PHYs,
>>>> which is handled by cdn_dp_switch_port() and cdn_dp_enable().
>>>>
>>>> There are two cases:
>>>>
>>>> 1. Neither bridge is enabled. In this case, both bridges can
>>>> independently read the EDID, and the PHY port may switch before
>>>> reading the EDID.
>>>>
>>>> 2. One bridge is already enabled. In this case, other bridges are not
>>>> allowed to read the EDID. So we will try to return the cached EDID.
>>>>
>>>> Since the scenario of two ports plug in at the same time is rare,
>>>> I don't have a board which support two TypeC connector to test this.
>>>> Therefore, I tested forced switching on a single PHY port, as well as
>>>> output using a fake PHY port alongside a real PHY port.
>>>>
>>>> Signed-off-by: Chaoyi Chen <chaoyi.chen@rock-chips.com>
>>>> ---
>>>>
>>>> + /* One endpoint may correspond to one HPD bridge. */
>>>> + for_each_of_graph_port_endpoint(port, dp_ep) {
>>>> + struct device_node *phy_bridge_node __free(device_node) =
>>>> + of_graph_get_remote_port_parent(dp_ep);
>>>> +
>>>> + bridge = of_drm_find_bridge(phy_bridge_node);
>>>> + if (!bridge) {
>>>> + ret = -EPROBE_DEFER;
>>>> + goto out;
>>>> + }
>>>> +
>>>> + dp->hpd_bridge_valid = true;
>>>> + dp->hpd_bridge_list[count].bridge = bridge;
>>>> + dp->hpd_bridge_list[count].parent = dp;
>>>> + dp->hpd_bridge_list[count].id = count;
>>> This looks misnamed. They are not necessarily HPD bridges. There can be
>>> a random chain between your controller and the actual output / connector
>>> /etc.
>> Yes, and more precisely, this should be `pervious_bridge_list` . Will fix in v6.
> I think the typical convention is around next_bridge, not previous.

Oh, that's true.  Will fix this in v6.

>
>
--
Best,
Chaoyi