On 2015年05月14日 22:44, David Laight wrote:
From: Rodrigo Severo
Sent: 14 May 2015 15:06
Activating XHCI_TRUST_TX_LENGTH on Renesas uPD720201 USB 3.0 hosts to get rid of
the following warnings when using webcams on this type of host:
xhci_hcd 0000:06:00.0: WARN Successful completion on short TX: needs
XHCI_TRUST_TX_LENGTH quirk?
Given that the driver always reads the receive data length (in order
to output the message) is there any reason not to make the 'quirk'
the default behaviour?
I don't think this is a default behavior. In this quirk case, xHC reports
that it has completed a transfer _successfully_, but there are still some
bytes _not_ transfered yet.
Driver needs a hardware quirk to decide "which one should I trust, transfer
completed successfully, or only part of data has been transfered?"
If hardware completes a transfer successfully, it should set "Successful"
to "completion code" and set "TRB transfer length" to 0.
If hardware completes result in a short package transfer, it should set
"Short Packet" to "completion code" and set "TRB transfer length" to the
length of data that was not transmitted.
If hardware completes result in an error, it should set completion code
as the error code and set "TRB transfer length" to the length of data that
was not transmitted.
Thanks,
-Baolu
To put it another way, has anyone ever seen hardware that reports
a successful completion of a full length transfer and writes a
short length into descriptor?
This would result in the above message when the quirk wasn't
required.
Note that the probably ought to have been names 'TRUST_RX_LENGTH'
since the driver then uses the length written into the rx descriptor.
This has nothing to do with any 'length' field received from the
remote system (except that implied by the amount of data).
David
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