[Bug 222188] New: ASUS ROG Flow Z13 GZ302EAC (Strix Halo): no DisplayPort Alt Mode on USB4 Type-C ports, partner altmodes never registered by UCSI

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=222188

            Bug ID: 222188
           Summary: ASUS ROG Flow Z13 GZ302EAC (Strix Halo): no
                    DisplayPort Alt Mode on USB4 Type-C ports, partner
                    altmodes never registered by UCSI
           Product: Drivers
           Version: 2.5
          Hardware: AMD
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: USB
          Assignee: drivers_usb@kernel-bugs.kernel.org
          Reporter: dimitri.creus@gmail.com
        Regression: No

Created attachment 311261
  --> https://bugzilla.kernel.org/attachment.cgi?id=311261&action=edit
rapport-usbc.txt

Hardware: ASUS ROG Flow Z13 GZ302EAC (AMD Ryzen AI Max+ 395, Radeon 8060S
"Strix Halo"), BIOS GZ302EAC.304.
Both Type-C ports are USB4 with DisplayPort and Power Delivery according to
ASUS specifications.

Problem:
A passive USB-C -> HDMI cable (DP Alt Mode) connected to a TV gives no picture.
All card1-DP-* DRM
connectors stay "disconnected". The native HDMI port of the same laptop works
with the same TV.
The same cable and TV work with another DP Alt Mode source (Meta Quest 3), so
cable and display are fine.

Observations (Fedora 44, kernel 7.2.11-200.fc44):
- typec, typec_ucsi, ucsi_acpi are loaded; typec_displayport was not
auto-loaded.
- The cable is enumerated as a port partner (portN-partner appears on plug and
disappears on unplug),
  supports_usb_power_delivery=yes, power_role source, data_role host.
- No partner altmode is ever registered: /sys/bus/typec/devices/ stays empty.
- Loading typec_displayport manually and re-plugging changes nothing.
- Same result on both Type-C ports, both plug orientations, cold boot with the
cable connected,
  and after an ASUS EC reset.
- Nothing typec/ucsi related is logged by the kernel on plug or unplug.

Also reproduced with an Ubuntu 26.10 live USB (kernel 7.3): same behaviour, no
picture.

Expected: DisplayPort Alt Mode entered, a DP connector becomes "connected".

Attached: rapport-usbc.txt (typec sysfs attributes, port and partner altmodes,
partner identity,
DRM connector status, lspci, kernel log filtered on
ucsi/typec/thunderbolt/usb4).

I can test patches or provide more debug output (ucsi tracing, debugfs) if
needed.

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