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[Bug 1859378] Re: xhci Control Transfer requiring a Status TRB before st

From: Benjamin David Lunt
Subject: [Bug 1859378] Re: xhci Control Transfer requiring a Status TRB before starting transfer
Date: Mon, 13 Jan 2020 00:30:07 -0000

Removing this check will indeed require a bit of a re-write.  The way
the code is now, the transfer expects a SETUP packet to be first.  If
you remove the check I ask about above, will the next transfer show that
it is the STATUS packet?  If so, then the check at line 1696 will indeed
catch and not allow the STATUS packet to be accepted.

A little more work might need to be done to remove this check.

It is just a request.

Thank you,

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  xhci Control Transfer requiring a Status TRB before starting transfer

Status in QEMU:

Bug description:
  This may not necessarily be a bug, but more of a change.

  A little background may need to be in order.

  With all USB Control transfers, there is a SETUP transfer, zero or
  more DATA transfers, and if successful, a STATUS transfer.  This
  STATUS transfer is used to indicate to the recipient that the previous
  transfers were successful.  For example, in a CONTROL IN transfer, the
  host sends a SETUP packet to the device, receives zero or more DATA
  packets, and then on successful transfer, the HOST sends the STATUS
  packet indicating to the device that all was received.

  If no DATA packets are received, the HOST is not to send a STATUS
  packet.  This could be due to a STALL or other error.

  With this in mind, the STATUS transfer, in this case an xHCI STATUS
  TRB, may not even be on the transfer ring yet.  The HOST software may
  be waiting for a successful transfer before it submits the STATUS

  However, if you look at the test at line 1701
  the current code will not start the CONTROL transfer at all if it
  doesn't see that STATUS TRB on the ring.

  In my opinion, this is in error.  It is not required that a STATUS TRB
  be on the ring to start the CONTROL transfer.  This STATUS TRB can be
  placed on the ring after a successful SETUP and zero or more DATA
  transfers followed by a ring to the door bell.  Then after a
  successful transfer to this point, placing this STATUS TRB on the ring
  and another ring to the door bell.

  In my opinion, the check at line 1701 should be removed.

  Thank you,

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