On Wed, Jul 3, 2013 at 10:15 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Wed, 3 Jul 2013, Ming Lei wrote: > >> >> Yes, that is the change tasklet is bringing, so looks we need to find a way >> >> to distinguish streaming-on from underrun when stream->td_list becomes >> >> empty in iso_stream_schedule(). >> > >> > The difference will be the URB_ISO_ASAP flag. The flag should be set >> > in the first URB of a new stream. It should not be set in any other >> > URBs, unless the client driver doesn't care about losing >> > synchronization when an underrun occurs. >> >> So sounds a better name for the flag should be URB_ISO_STREAM_ON, :-) > > I agree, but the existing name is already exposed to userspace in > include/uapi/linux/usbdevice_fs.h. We could change the internal name 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. > while leaving the external name the same, but that would be confusing. > > (URB_ISO_ASAP used to mean that the HCD was responsible for scheduling > the URB, and if the flag wasn't set then the value of urb->start_frame > would be used directly. This doesn't make sense, because drivers > should not be in charge of URB scheduling -- HCDs should take care of > it. So I have felt free to alter the flag's meaning.) Anyway the name will become a bit confusing, so if we don't plan to change it, we should add detailed comment about its usage. > >> Also looks drivers need fix for the API change. > > I don't know if any drivers will need to be fixed. I suspect many of Since the flag was exported to userspace, it is really hard to know now, :-) > them simply set URB_ISO_ASAP on all their URBs. Clemens has already > added a fix for the snd-usb-audio driver. I am wondering the fix has been added because it may depend on the coming change of URB_ISO_ASAP, :-) 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
