On 04/11/2017 12:45 AM, Felipe Balbi wrote: > > Hi, > > John Youn <John.Youn@xxxxxxxxxxxx> writes: >>> Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx> writes: >>>> The dwc3 driver can overwite its previous events if its top half IRQ >>>> handler gets invoked again before processing the events in the cache. We >>> >>> interrupts are masked, why would top half get invoked again? Is this, >>> perhaps, related to DWC3 3.00a which has the "Interrupt line doesn't >>> lower when masked" problem? We've added a lot of code to workaround that >>> problem and, apparently, it wasn't enough. >> >> No, it is not related to that. We verified with PCIe traces. The >> interrupt line gets deasserted after we mask it. And we put the >> masking as close to the beginning of the top-half as possible. >> >>> >>> In any case, there's no way top half would be invoked again in a >>> properly working DWC3. >> >> Yet we still see it sometimes. Usually it doesn't create a problem, > > that's fair, but it's not for the reason you're describing :-) There > might be another problem going on, because since we masked the interrupt > and cleared all events, IRQ shouldn't be raised at all; unless, as I > mentioned on the other subthread, the IRQ line is shared. > >> but if there happens to be a new event there, we get the failure. >> >> We didn't trace into that part of the kernel so we can't explain why. >> But if there is any chance the interrupt line deassertion wasn't >> detected in time, whatever part of the kernel that thinks it is still >> asserted might just call our top-half again. This could be a totally >> wrong assumption, but it doesn't seem too far-fetched. > > The kernel doesn't detect IRQ line assertion/deassertion. CPU gets an > exception when that happens and calls Kernel IRQ handler vector. That > will, in turn, figure out which line triggered, call the handler and so > on. We're talking about PCIe though, where interrupt assertion and deassertion are packets. So I would imagine the kernel has to do something and there could be some latency associated with that. John -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
