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

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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





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