On Fri, Oct 01, 2021 at 03:26:48AM +0000, Hayes Wang wrote:

quoted

Alan Stern [off-list ref]
[...]

quoted

There has been some discussion about this in the past.

In general, -EPROTO is almost always a non-recoverable error.

Excuse me. I am confused about the above description.
I got -EPROTO before, when I debugged another issue.
However, the bulk transfer still worked after I resubmitted
the transfer. I didn't do anything to recover it. That is why
I do resubmission for -EPROTO.

I check the Linux driver and the xHCI spec.
The driver gets -EPROTO for bulk transfer, when the host
returns COMP_USB_TRANSACTION_ERROR.
According to the spec of xHCI, USB TRANSACTION ERROR
means the host did not receive a valid response from the
device (Timeout, CRC, Bad PID, unexpected NYET, etc.).

That's right.  If the device and cable are working properly, this 
should never happen.  Or only extremely rarely (for example, caused 
by external electromagnetic interference).

It seems to be reasonable why resubmission sometimes works.

Did you ever track down the reason why you got the -EPROTO error 
while debugging that other issue?  Can you reproduce it?

Alan Stern

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