linux-kernel - Re: [PATCH 2/3] xhci: Fix control transfer error on Etron xHCI host

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Message-ID: <20240911095233.3e4d734d@foxbook>
Date: Wed, 11 Sep 2024 09:52:33 +0200
From: Michał Pecio <michal.pecio@...il.com>
To: ki.chiang65@...il.com
Cc: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
 linux-usb@...r.kernel.org, mathias.nyman@...el.com, stable@...r.kernel.org
Subject: Re: [PATCH 2/3] xhci: Fix control transfer error on Etron xHCI host

Hi,

> This happens when the xHCI driver enqueue a control TD (which cross
> over the Link TRB between two ring segments, as shown) in the endpoint
> zero's transfer ring. Seems the Etron xHCI host can not perform this
> TD correctly, causing the USB transfer error occurred, maybe the upper
> driver retry that control-IN request can solve problem, but not all
> drivers do this.
> 
> |     |
> -------
> | TRB | Setup Stage
> -------
> | TRB | Link
> -------
> -------
> | TRB | Data Stage
> -------
> | TRB | Status Stage
> -------
> |     |

I wonder about a few things.

1. What are the exact symptoms, besides Ethernet driver errors?
Any errors from xhci_hcd? What if dynamic debug is enabled?

2. How did you determine that this is the exact cause?

3. Does it happen every time when a Link follows Setup, or only
randomly and it takes lots of control transfers to trigger it?

4. How is it even possible? As far as I see, Linux simply queues
three TRBs for a control URB. There are 255 slots in a segemnt,
so exactly 85 URBs should fit, and then back to the first slot.

Regards,
Michal