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

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Message-ID: <20251210074133.GE2275908@black.igk.intel.com>
Date: Wed, 10 Dec 2025 08:41:33 +0100
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: "Chia-Lin Kao (AceLan)" <acelan.kao@...onical.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,
	Mario Limonciello <mario.limonciello@....com>, Sanath.S@....com
Subject: Re: [PATCH] [RFC] thunderbolt: Add delay for Dell U2725QE link width

Hi,

On Wed, Dec 10, 2025 at 11:15:25AM +0800, Chia-Lin Kao (AceLan) wrote:
> > We should understand the issue better. This is Intel Goshen Ridge based
> > monitor which I'm pretty sure does not require additional quirks, at least
> > I have not heard any issues like this. I suspect this is combination of the
> > AMD and Intel hardware that is causing the issue.
> Actually, we encountered the same issue on Intel machine, too.
> Here is the log captured by my ex-colleague, and at that time he used
> 6.16-rc4 drmtip kernel and should have reported this issue somewhere.
> https://paste.ubuntu.com/p/bJkBTdYMp6/
> 
> The log combines with drm debug log, and becomes too large to be
> pasted on the pastebin, so I removed some unrelated lines between 44s
> ~ 335s.

Okay I see similar unplug there:

[  337.429646] [374] thunderbolt:tb_handle_dp_bandwidth_request:2752: thunderbolt 0000:00:0d.2: 0:5: handling bandwidth allocation request, retry 0
...
[  337.430291] [165] thunderbolt:tb_cfg_ack_plug:842: thunderbolt 0000:00:0d.2: acking hot unplug event on 0:1

We had an issue with MST monitors but that resulted unplug of the DP OUT
not link going down. That was fixed with:

  9cb15478916e ("drm/i915/dp_mst: Work around Thunderbolt sink disconnect after SINK_COUNT_ESI read")

If you have Intel hardware still there it would be good if you could try
and provide trace from that as well.