On Tue, 3 Sep 2013, Greg KH wrote: > 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? That's understandable. It's not necessary to revert all the tasklet changes. The only one that matters is commit 428aac8a8105 (USB: EHCI: support running URB giveback in tasklet context). Without that one, the tasklet mechanism will be present but not used. It's also okay to keep Ming Lei's other changes to ehci-hcd; they are compatible with operation either with or without tasklets. Alan Stern -- 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
