On Tue, Sep 03, 2013 at 01:58:23PM -0400, Alan Stern wrote: > Greg: > > This series of three patches modifies the isochronous scheduling > routine in ehci-hcd, adding changes that we need for proper operation > with tasklets (with a new inline routine needed in usbcore). > > The problem is that we have to maintain the existing API guarantee that > URBs submitted in a completion handler will keep an isochronous stream > alive, maintaining synchronization with the device. Until recently > this wasn't an issue; URBs submitted by a completion handler would be > processed while the giveback operation was in progress, so the endpoint > queue would never appear to be empty. > > But now completion handlers run in a separate tasklet context. The > giveback operation will end before the completion handler runs and > submits any URBs. Therefore we need a way to tell whether a particular > URB submission was made by a completion handler, and we need to handle > the case where the endpoint queue does empty out temporarily. > > That's what these patches do. The first one adds a mechanism to > usbcore for determining whether an endpoint's completion handler is > running. The other two modify ehci-hcd to do the right thing when the > queue gets an underrun. > > These changes are intended to avoid bad side effects in the USB audio > driver when interrupt latency causes a delay in the isochronous stream. > Since the tasklet changes have already been accepted, I think these > patches will also need to go to Linus before the current merge window > closes. It's really late in the merge window cycle (i.e. it's already started) to be taking patches that mess with the EHCI scheduling code. I'd rather just revert the tasklet changes if they are causing the problem here, and then hold off for all of this until 3.13, would that be ok? thanks, greg k-h -- 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
