Re: thunderbolt: DP tunnel activation not retried when display NAKs while settling after link reset (Apple Studio Display XDR 2026 on Panther Lake)

[Imre Deak <imre.deak@intel.com>]

Hi Dennis,

thanks for the logs.

Could you confirm that the problem you see is:

After boot-up with both displays connected, one of the display is blank
by 4.839037, while the other display lights up okay.

By 47.768154 both displays light up correctly.

I can't see any obvious issues related to tunneling, both tunnels are
detected and the BW allocations for them succeed as expected.

Could you try if the same sequence without the other issue you mentioned
happening (DP tunnel activation failed) the blank screen problem
reproduces booting with: xe.enable_fbc=0 ?

Thanks,
Imre

On Tue, Aug 25, 2026 at 09:42:23AM +0800, Dennis Wang wrote:
> Hi Mika, Imre,
> 
> Attached: cold boot dmesg with thunderbolt.dyndbg=+p + drm.debug=0x10e
> (timestamps rebuilt from _SOURCE_MONOTONIC_TIMESTAMP; root fs is LUKS
> so journald re-stamps initramfs kmsg).
> 
> This boot hit the graphics-side flavor - tunnels healthy, screen black
> until the LUKS passphrase was typed blind at ~40 s:
> 
>   1.8s   XDR found, Gen3 x2, both DP tunnels allocated, no errors
>   3.9s   second sink (0:10 <-> 3:12): repeated "DPRX read timeout"
>          (tiled 2x1 panel, two DP sinks)
>   3.96s  fastset rejected: crtc_hblank_start expected 3840, found 1920
>   11.3s  AUX_TC2 power well disabled - nothing lights the panel again
>          until the compositor modeset after unlock (~60 s)
> 
> A control cold boot with video=DP-2:d (masking the second sink) is
> fully clean, panel lit at ~4 s, single-stream 5K120 DSC. The original
> "DP tunnel activation failed" flavor is intermittent - will send it
> with full debug when I catch it.
> 
> Happy to test patches on this hardware.
> 
> Thanks,
> Dennis Wang