Re: DP routing from iGPU to discrete Barlow Ridge TB5 on HP ZBook Fury G1i

Rodrigo Vivi
2026-04-20T20:47:36Z

On Mon, Apr 20, 2026 at 04:04:02PM +0000, Francesco Orro wrote:
> Hi,
>
> Setup:
> HP ZBook Fury G1i 16 inch, BIOS X96 01.03.04
> Intel Arrow Lake-HX + Nvidia RTX PRO 1000 Blackwell (hybrid graphics)
> Kernel 6.19.13
>
> The laptop exposes Thunderbolt 5 on both the integrated MTL iTBT (right
> USB-C, domain0, 00:0d.2) and a discrete Intel Barlow Ridge (left USB-C,
> domain1, 00:06.1 -> 05:00.0).
>
> - Right port: i915 drives a DP tunnel over the iTBT host without issues.
> - Left port: no i915 connector ever sees the external monitor. The TB
> driver allocates a DP tunnel on demand but DPRX reads time out, no DP
> source is feeding the Barlow DP_IN adapter.
> - With nvidia-drm.modeset=1, a DP-MST connector on the Nvidia DRM device
> sees the monitor via the left port (EDID readable, modes negotiated).
> The path Nvidia -> Barlow DP_IN is functional.
>
> Current hypothesis: on this board the discrete Barlow Ridge DP_IN is
> either hardwired to a Nvidia output or behind a firmware-programmed mux
> that BIOS latches to Nvidia at POST and is not exposed to the OS. i915
> would therefore have no path to drive the left ports, by design.

yes, that is usually the case.

>
> Tests done that did not surface an OS-visible lever:
> - i2cdetect across all SMBus/i801 busses: no DP mux/retimer at plausible
> addresses (0x60-0x7F).
> - DSDT/SSDT dump (iasl -d): no Device/Method referring to DP routing,
> DPMUX, retimer programming, or dock display source selection.
> - HP WMI + /sys/devices/virtual/firmware-attributes/hp-bioscfg attribute
> enumeration: nothing switching dock display source. "Graphics"
> attribute only offers Hybrid/Discrete.
> - PCI config dump of Barlow Ridge: standard USB4 NHI, no vendor-specific
> capability hinting at source selection.
> - acpi.no_usb4_osc kernel param (locally patched) to opt out of OSC USB4
> native support: no change in i915 visibility of the dock.
>
> Is there any known way to route an Intel DDI output to a PCIe-attached
> Barlow Ridge DP_IN adapter, or is this strictly a design where the dGPU
> is the only valid DP source for the discrete TB controller on this class
> of HP workstations?

I believe this is physically connected or static mux without any way to
re-route this. But I might be wrong.

So, bringing some more folks to the discussion.

>
> Happy to share the DSDT dump, lspci -vvv, full dmesg, or run any test.
>
> Regards,
> Francesco Orro