Re: [PATCH] [RFC] thunderbolt: Add delay for Dell U2725QE link width

[Mika Westerberg]

On Mon, Dec 22, 2025 at 09:33:48AM +0800, Chia-Lin Kao (AceLan) wrote:
> On Thu, Dec 18, 2025 at 11:20:21AM +0100, Mika Westerberg wrote:
> > On Thu, Dec 18, 2025 at 03:35:05PM +0800, Chia-Lin Kao (AceLan) wrote:
> > > > Now since USB 2.x has its own wires in Type-C cable this tells me that
> > > > there is some real problem with the connection. Have you tried different
> > > > cables already?
> > > Here is the log I got with another tbt4 cable.
> > > I'm using the kernel with Mario suggests modification.
> > > 
> > > https://people.canonical.com/~acelan/bugs/tbt_call_trace/intel/merged_6.18.0-d358e5254674+.patched2.2_new_cable.out
> > 
> > Here I see (assuming I read it right) that the USB 2.x enumerates only
> > after the first unplug:
> > 
> > [   28.589861] usb 3-2: New USB device found, idVendor=1d5c, idProduct=5801, bcdDevice= 1.01
> > [   28.589864] usb 3-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
> > [   28.589865] usb 3-2: Product: USB2.0 Hub
> > [   28.589866] usb 3-2: Manufacturer: Fresco Logic, Inc.
> >From the logs, sometimes this hub is enumerated before the call trace
> and then enumerated again after the call trace.
> 
> And I also found there are some suspicious USB disconnections while
> plugging in the tbt monitor.
> 
> I tried to avoid the USB disconnection by the following modification,
> but still no luck.

Okay but I think this is not a SW issue, rather an issue with that
particular monitor/cable/connection/PD. It is not just the USB4 link that
goes down it's the whole type-C connection therefore something is wrong on
the electrical side of things (well at least it seems so).

Dell also typically validate that their stuff works in Linux so I would
expect to got some report from them if that's not the case (unless you are
doing just that ;-))

Have you tried this same monitor with Windows? Do you see the same issue
there? I would expect so.