Hello,

On 1/26/2026 3:42 AM, Hugh Cole-Baker wrote:

On 19/01/2026 07:30, Chaoyi Chen wrote:

quoted

From: Chaoyi Chen <redacted>

This series focuses on adding Type-C DP support for USBDP PHY and DP
driver. The USBDP PHY and DP will perceive the changes in cable status
based on the USB PD and Type-C state machines provided by TCPM. Before
this, the USBDP PHY and DP controller of RK3399 sensed cable state
changes through extcon, and devices such as the RK3399 Gru-Chromebook
rely on them. This series should not break them.

====
1. DisplayPort HPD status notify

Before v7, I implemented a variety of DP HPD status notify. However,
they all had various problems and it was difficult to become a generic
solution.

Under the guidance of Heikki and Dmitry, a decoupled notification
method between the TypeC and DRM subsystems was introduced in v7.
First, a notification is sent when TypeC registers a new altmode.
Then, a generic DP AUX HPD bridge is implemented on the DRM side.

During v7-v10, we added a new notifier in typec to notify the altmode
device register event. With the help of Greg and Heikki, we implemented
the reuse of notifiers for the type bus itself in patch1 of v11.

The USB subsystem related parts have already been merged into the
usb-next branch in v13 [0][1]. Therefore, this series no longer includes
these patches starting from v14. Thanks to Greg and Heikki!

[0]: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git/commit/?h=usb-next&id=67ab45426215c7fdccb65aecd4cac15bbe4dfcbb
[1]: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git/commit/?h=usb-next&id=4dee13db29de6dd869af9b3827e1ff569644e838

That makes it redundant for each Type-C controller driver to implement
a similar DP AUX HPD bridge in embedded scenarios.

====
2. Altmode switching and orientation switching for USBDP PHY

For USB Type-C interfaces, an external Type-C controller chip assists
by detecting cable attachment, determining plug orientation, and
reporting USB PD message. The USB/DP combo PHY supports software
configurable pin mapping and DisplayPort lane assignment. Based on
these message, the combo PHY can perform both altmode switching and
orientation switching via software.

The RK3399 EVB IND board has a Type-C interface DisplayPort. It use
fusb302 chip as Type-C controller. The connection diagram is shown below:

fusb302 chip +---> USB2.0 PHY ----> DWC3 USB controller
             |
             +---> USB/DP PHY0 +--> CDN-DP controller
                               |
                               +--> DWC3 USB controller

====
3. Multiple bridge model for RK3399 CDN-DP

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.

USB/DP PHY0 ---+
               | <----> CDN-DP controller
USB/DP PHY1 ---+

In previous versions, if both PHY ports were connected to DP,
the CDN-DP driver would select the first PHY port for output.

On Dmitry's suggestion, we introduced a multi-bridge model to support
flexible selection of the output PHY 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. And Once the first bridge is obtained, we can get the
last bridge corresponding to the USB-C connector, and then set the
DRM connector's fwnode to the corresponding one to enable HPD
notification.

With a similar dts patch [1] on top of this series I tested a type-C to
DP adapter/cable for display output on the ROCKPro64 board, which also
pairs a FUSB302 with RK3399. Booting it up with the cable plugged in
works, as does hotplugging the cable after booting in both orientations.
The correct mode for the display is detected. I wasn't able to test
audio, only video output, as this display doesn't have speakers.

I did once, after unplugging and reconnecting the cable a few times,
see it get into a state where it didn't detect the attached display.
Logs from that unplug/reconnect attempt are here [2] if of interest.
Nevertheless, hotplug seems to work the majority of the time, so

Tested-by: Hugh Cole-Baker <redacted>

[1]: https://github.com/sigmaris/linux/commit/91724088b19bee7d248946442a801423e8cd0634
[2]: https://gist.github.com/sigmaris/fa107384a7492583ceee1c2962f5030a

Thank you for the test. I also have the same board, and I will
try it later :)

-- 
Best, 
Chaoyi