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

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 11.9.2024 8.17, Kuangyi Chiang wrote:
> Performing a stability stress test on a USB3.0 2.5G ethernet adapter
> results in errors like this:
> 
> [   91.441469] r8152 2-3:1.0 eth3: get_registers -71
> [   91.458659] r8152 2-3:1.0 eth3: get_registers -71
> [   91.475911] r8152 2-3:1.0 eth3: get_registers -71
> [   91.493203] r8152 2-3:1.0 eth3: get_registers -71
> [   91.510421] r8152 2-3:1.0 eth3: get_registers -71
> 
> The r8152 driver will periodically issue lots of control-IN requests
> to access the status of ethernet adapter hardware registers during
> the test.
> 
> 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
> -------
> |     |
> 

What if the link TRB is between Data and Status stage, does that
case work normally?

> To work around this, the xHCI driver should enqueue a No Op TRB if
> next available TRB is the Link TRB in the ring segment, this can
> prevent the Setup and Data Stage TRB to be breaked by the Link TRB.

There are some hosts that need the 'Chain' bit set in the Link TRB,
does that work in this case?

Thanks
Mathias