linux-kernel - Re: [PATCH] thunderbolt: Fix PCIe device enumeration with delayed rescan

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Message-ID: <20260121060142.GJ2275908@black.igk.intel.com>
Date: Wed, 21 Jan 2026 07:01:42 +0100
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: "Chia-Lin Kao (AceLan)" <acelan.kao@...onical.com>
Cc: 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
Subject: Re: [PATCH] thunderbolt: Fix PCIe device enumeration with delayed
 rescan

Hi,

On Wed, Jan 21, 2026 at 01:27:44PM +0800, Chia-Lin Kao (AceLan) wrote:
> PCIe devices behind Thunderbolt tunnels may fail to enumerate when
> spurious hotplug events prevent pciehp from detecting link-up.
> 
> Root cause:
> 
> Spurious unplug events occur immediately after tunnel activation:
> 
>   [  932.438] thunderbolt: acking hot unplug event on 702:2
>   [  932.852] thunderbolt: PCIe Up path activation complete
>   [  932.855] thunderbolt: hotplug event for upstream port 702:2
>             (unplug: 0)
>   [  932.855] thunderbolt: hotplug event for upstream port 702:2
>             (unplug: 1)
> 
> These events disrupt pciehp timing, causing device enumeration to fail
> ~70% of the time on affected hardware. Manual PCI rescan succeeds,
> proving devices are present and functional on the bus.

Thanks for the report!

They are likely TB3 xHCI "plug" events or so but they should not affect
anything really.

It may be that there is something in the TB3 compatibility side that we are
not doing which needs to be investigated.

>From your merged.out.bad:

CM does xHCI connect here:

[  152.905840] [182] thunderbolt 0000:c7:00.6: 702: xHCI connect request
[  152.906865] [182] thunderbolt 0000:c7:00.6: hotplug event for upstream port 702:2 (unplug: 0)
[  152.906869] [182] thunderbolt 0000:c7:00.6: 2:8: got plug event for connected port, ignoring
[  152.906872] [182] thunderbolt 0000:c7:00.6: hotplug event for upstream port 702:2 (unplug: 1)
[  152.906875] [182] thunderbolt 0000:c7:00.6: 2:8: got unplug event for disconnected port, ignoring

[  192.931373] [49] thunderbolt 0000:c7:00.6: acking hot unplug event on 2:7

Can you comment out call to tb_switch_xhci_connect() and see if that
changes anything?

> Solution:
> 
> Schedule delayed work (300ms) after tunnel activation to:
> 1. Check if pciehp successfully enumerated devices (device count increased)
> 2. If not, trigger pci_rescan_bus() to discover devices manually
> 3. Log results for observability
> 
> The delayed work approach is non-blocking and only rescans when actually
> needed, avoiding overhead on systems where pciehp works correctly.

There is no way we are going to call PCI functions from the tb.c.