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

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Message-ID: <20251218072125.GU2275908@black.igk.intel.com>
Date: Thu, 18 Dec 2025 08:21:25 +0100
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: AceLan Kao <acelan.kao@...onical.com>
Cc: Mario Limonciello <mario.limonciello@....com>,
	Andreas Noever <andreas.noever@...il.com>,
	Mika Westerberg <westeri@...nel.org>,
	Yehezkel Bernat <YehezkelShB@...il.com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, Sanath.S@....com,
	"Lin, Wayne" <Wayne.Lin@....com>
Subject: Re: [PATCH] [RFC] thunderbolt: Add delay for Dell U2725QE link width

Hi,

On Thu, Dec 18, 2025 at 09:38:13AM +0800, AceLan Kao wrote:
> > > +     /*
> > > +      * Scan for downstream retimers. We only scan them after the
> > > +      * router has been enumerated to avoid issues with certain
> > > +      * Pluggable devices that expect the host to enumerate them
> > > +      * within certain timeout.
> > > +      */
> > > +     tb_retimer_scan(port, true);
> Hi Mika,
> 
> This doesn't work.
> https://people.canonical.com/~acelan/bugs/tbt_call_trace/intel/merged_6.18.0-d358e5254674+.patched1.out

Okay thanks for trying. I noticed that there is also USB 2.x disconnect:

[    4.470610] usb 3-2: New USB device found, idVendor=1d5c, idProduct=5801, bcdDevice= 1.01
[    4.470618] usb 3-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[    4.470620] usb 3-2: Product: USB2.0 Hub
[    4.470622] usb 3-2: Manufacturer: Fresco Logic, Inc.
...
[  104.699872] tb_tx Read Request Domain 0 Route 303 Adapter 0
               0x00/---- 0x00000000 0b00000000 00000000 00000000 00000000 .... Route String High
               0x01/---- 0x00000303 0b00000000 00000000 00000011 00000011 .... Route String Low
               0x02/---- 0x0400202c 0b00000100 00000000 00100000 00101100 ...,
                 [00:12]       0x2c Address
                 [13:18]        0x1 Read Size
                 [19:24]        0x0 Adapter Num
                 [25:26]        0x2 Configuration Space (CS) → Router Configuration Space
                 [27:28]        0x0 Sequence Number (SN)
[  104.700850] tb_event Hot Plug Event Packet Domain 0 Route 0 Adapter 3 / Lane
               0x00/---- 0x80000000 0b10000000 00000000 00000000 00000000 .... Route String High
               0x01/---- 0x00000000 0b00000000 00000000 00000000 00000000 .... Route String Low
               0x02/---- 0x80000003 0b10000000 00000000 00000000 00000011 ....
                 [00:05]        0x3 Adapter Num
                 [31:31]        0x1 UPG
[  104.700852] [763] thunderbolt 0000:00:0d.2: acking hot unplug event on 0:3

// Here we got the unplug to 0:3. After a while

[  106.844134] usb 3-2: USB disconnect, device number 14

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?