I believe it is required to send an error event. It checked for the STATUS TRB and found that it was missing, therefore it must send an Error Event.
This is (not so clearly) stated in the specification and I have quoted this in a previous comment. I took it as: If the controller checks for the error and then does not processes the transfer due to the check, the controller is required to place an Error Event on the Event ring. Therefore, QEMU either needs to follow through with the check and place an Error on the Event Ring *or* not do the 'check and return'. Anyway, this is just my opinion. Thank you for your time. Ben -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1859378 Title: xhci Control Transfer requiring a Status TRB before starting transfer Status in QEMU: Invalid 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 transfer. However, if you look at the test at line 1701 (https://git.qemu.org/?p=qemu.git;a=blob;f=hw/usb/hcd-xhci.c#l1701), 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, Ben To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1859378/+subscriptions
