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

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Message-ID: <4634177b-8ed1-4d65-9f3c-754d8c1eb828@amd.com>
Date: Wed, 10 Dec 2025 15:42:21 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: Mika Westerberg <mika.westerberg@...ux.intel.com>,
 "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, Sanath.S@....com,
 "Lin, Wayne" <Wayne.Lin@....com>
Subject: Re: [PATCH] [RFC] thunderbolt: Add delay for Dell U2725QE link width

+Wayne

Here is the full thread since you're being added in late.

https://lore.kernel.org/linux-usb/20251209054141.1975982-1-acelan.kao@canonical.com/

On 12/10/25 1:41 AM, Mika Westerberg wrote:
> 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.

If that does help; we could experiment with doing something similar in 
amdgpu too.

It would mean it's not really an iTBT DP-in adapter's firmware issue in 
that case.

Acelan,

If you want to try to port 9cb15478916e over the interrupt handler in 
amdgpu that needs the change I expect to be dp_read_hpd_rx_irq_data().