On Mon, 22 Aug 2016, Bjørn Mork wrote: > Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> writes: > > > On Sun, 21 Aug 2016, Jiri Slaby wrote: > > > >> Cc: proper lists. > >> > >> ep->desc.bInterval seems to be 0 here. > > As far as I can see, this isn't possible. The usb_parse_endpoint() > > routine in drivers/usb/core/config.c is supposed to guarantee that > > ep->desc.bInterval is never 0. > > That is if it is an ISO endpoint, right? I can't tell; the bug report doesn't say. However, ep->desc.bInterval is ignored for bulk and control endpoints, so it must be either isochronous or interrupt. > Maybe I misunderstand something fundamental, but the "||" strikes me as > odd here: > > as->urb->stream_id = stream_id; > if (uurb->type == USBDEVFS_URB_TYPE_ISO || > ps->dev->speed == USB_SPEED_HIGH) > as->urb->interval = 1 << min(15, ep->desc.bInterval - 1); > else > as->urb->interval = ep->desc.bInterval; > as->urb->context = as; No, that's right (mostly -- we really should check for ps->dev->speed >= USB_SPEED_SUPER as well as == USB_SPEED_HIGH). > Typo? USB uses two different encodings for endpoint intervals. The second encoding above just gives the interval in frames; this is used for low- and full-speed interrupt endpoints. The first encoding above is exponential (it gives n where the actual interval is 2^(n-1) frames or microframes); this is used for all isochronous endpoints and for high-speed (or SuperSpeed etc.) interrupt endpoints. See for example the definition of usb_fill_int_urb() in include/linux/usb.h. 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
