On Wed, 23 Jan 2019, Bin Liu wrote: > > One possibility is to giveback URBs with certain errors (such as > > -EPROTO) only at a frame boundary, or at 1-ms intervals. This feels > > like a very artificial solution, though. > > My plan is to add an error counter in musb driver endpoint struct, if > -EPROTO has happened consequentially for a certain times, for example 3, > giveback URBs with -EPIPE instead -EPROTO. This is the simplest solution > I can think of, though I hate expending struct unnecessarily, this is > one of the cases. But -EPIPE is documented to mean that the device replied with a STALL. You would be violating the documentation. > > > > I do see now that of all USB drivers we have two drivers that handles > > > > -EPROTO by resubmitting after a delay, while a handful explicitly deals > > > > with -EPROTO by simply stopping to resubmit (some probably bail out on > > > > all errors, but the majority appear to resubmit on -EPROTO). > > > > Any driver which immediately retries an URB after getting -EPROTO or > > -EILSEQ or -ETIME, and has no mechanism for backing off or limiting the > > retries, is buggy. As far as I can see, that's all there is to it. > > Agreed, but given that majority appear to resubmit on -EPROTO as Johan > said, I think better to handle it in HCD. Do all those other drivers handle -EPIPE correctly? A logical way to respond to -EPIPE is to issue a Clear-Halt request; what will happen when that also fails? I think it makes more sense to continue using -EPROTO but slow down the exchange of packets so that there is no interrupt storm. > > > Thanks for the info. > > > I will handle this case in musb driver. > > > > Why doesn't the same problem occur with other types of host controller? > > Not sure, I am on musb for most of the times. Maybe other HCD doesn't > giveback URBs with -EPROTO in such error case. ehci-hcd also uses -EPROTO. > musb controller has a register bit telling the controller has tried the > transaction 3 times but didn't receive any response, then the musb > driver just giveback this URB with -EPROTO. Same with EHCI. Alan Stern
