On 24.5.2021 22.23, Thinh Nguyen wrote: > Alan Stern wrote: >> On Mon, May 24, 2021 at 06:18:59PM +0300, Mathias Nyman wrote: >>> On 20.5.2021 23.30, Thinh Nguyen wrote: >>>> As for the xhci driver, there maybe a case where the stream URB never >>>> gets to complete because the transaction err_count is not properly >>>> updated. The err_count for transaction error is stored in ep_ring, but >>>> the xhci driver may not be able to lookup the correct ep_ring based on >>>> TRB address for streams. There are cases for streams where the event >>>> TRBs have their TRB pointer field cleared to '0' (xhci spec section >>>> 4.12.2). If the xhci driver doesn't see ep_ring for transaction error, >>>> it automatically does a soft-retry. This is seen from one of our >>>> testings that the driver was repeatedly doing soft-retry until the class >>>> driver timed out. >>>> >>>> Hi Mathias, maybe you have some comment on this? Thanks. >>> >>> This is true, if TRB pointer is 0 then there is no retry limit for soft retry. >>> We should add one and prevent a loop. after e few soft resets we can end with a >>> hard reset to clear the host side endpoint halt. >>> >>> We don't know the URB that was being tansferred during the error, and can't >>> give it back with a proper error code. >>> In that sense we still end up waiting for a timeout and someone to cancel >>> the urb. >> >> That's not good. There may not be a timeout; drivers expect transfers >> to complete with a failure, not to be retried indefinitely. >> >> However, if you do know which endpoint/stream the error is connected to, >> you should be able to get the URB. It will be the first one queued for >> that endpoint/stream. >> > > When the xhci can't recover a transfer with soft-retry, no outstanding > transfer can proceed/complete for the endpoint. If the TRB pointer is 0, > we just don't know which stream or endpoint ring it's for, but we know > all the outstanding URBs of an endpoint. Let's may as well return an > error status for all of them after a limited number of soft-retries. We get the endpoint, but not the stream. I guess we could walk through each stream of this endpoint, and return the first URB of every stream that has a pending URB. xHCI spec claims to supports 65533 streams per endpoint, but in real life UAS probably only uses a few per endpoint? -Mathias
