On Thu, Jul 18, 2013 at 3:24 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Thu, 4 Jul 2013, Alan Stern wrote: > >> On Thu, 4 Jul 2013, Ming Lei wrote: >> >> > >> If so, your coming change may break ABI because as you described >> > >> that "the flag should be set in the first URB of a new stream", but >> > >> some user-space drivers may not set it before. Even USB audio driver >> > >> doesn't set it in current -next tree. > > I had some more ideas about this. Instead of requiring drivers to set > URB_ISO_ASAP on just the first URB of an isochronous stream, we could > ask drivers to call usb_reset_endpoint() between streams. This would > tell the HCD that the next URB marks the start of a new stream, with no > need for a special flag. This idea still requires changes from old drivers. Also it might be not appropriate to call usb_reset_endpoint() in this case because other host controller's implementation may do other unnecessary thing for this situation. > > Another possibility, which would be even simpler, is for HCDs to assume > that if the endpoint's queue has been empty for more than 100 ms then a > new stream is starting. Then drivers wouldn't have to do anything > special at all. (Unless they are stopping and restarting streams very > rapidly, in which case something like usb_reset_endpoint() would be In this case, we may use changing altsetting to decide start of streaming. > necessary.) IMO, this one should be OK, and looks it is a bit similar with unlinking empty interrupt qh. Thanks, -- Ming Lei -- 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
