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

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Message-ID: <ca57d854-efd1-42b8-9c25-33b01aaf1065@rock-chips.com>
Date: Mon, 13 Oct 2025 10:44:53 +0800
From: Chaoyi Chen <chaoyi.chen@...k-chips.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Chaoyi Chen <kernel@...kyi.com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Vinod Koul <vkoul@...nel.org>,
 Kishon Vijay Abraham I <kishon@...nel.org>, Heiko Stuebner
 <heiko@...ech.de>, Sandy Huang <hjc@...k-chips.com>,
 Andy Yan <andy.yan@...k-chips.com>,
 Yubing Zhang <yubing.zhang@...k-chips.com>,
 Frank Wang <frank.wang@...k-chips.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Amit Sunil Dhamne <amitsd@...gle.com>,
 Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Dragan Simic <dsimic@...jaro.org>, Johan Jonker <jbx6244@...il.com>,
 Diederik de Haas <didi.debian@...ow.org>,
 Peter Robinson <pbrobinson@...il.com>, linux-usb@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-phy@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v5 6/8] drm/rockchip: cdn-dp: Add multiple bridges to
 support PHY port selection

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@...k-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@...k-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