On Wed, 20 Jun 2018, Sebastian Andrzej Siewior wrote: > Laurent suggested that the kerneldoc documentation could state that > usb_fill_int_urb() can also be used for the initialisation of an > isochronous urb. The USB documentation in > Documentation/driver-api/usb/URB.rst already mentions this, some drivers > do so and there is no explicit usb_fill_iso_urb(). > > Suggested-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > --- > On 2018-06-20 17:14:53 [+0300], Laurent Pinchart wrote: > > > So you simply asking that the kerneldoc of usb_fill_int_urb() is > > > extended to mention isoc, too? > > > > That would be nice I think. > > here it is. > > include/linux/usb.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/usb.h b/include/linux/usb.h > index 4cdd515a4385..c3a8bd586121 100644 > --- a/include/linux/usb.h > +++ b/include/linux/usb.h > @@ -1657,7 +1657,8 @@ static inline void usb_fill_bulk_urb(struct urb *urb, > * the endpoint descriptor's bInterval value. > * > * Initializes a interrupt urb with the proper information needed to submit > - * it to a device. > + * it to a device. This function can also be used to initialize an isochronous > + * urb. No, no! This function can _help_ initialize an isochronous URB, but that's all. It would be better to create an explicit usb_fill_isoc_urb() routine, and even that would have to be incomplete. There are two problems with using usb_fill_int_urb() to initialize an isochronous URB: The calculation of the interval value is wrong for full-speed devices. The routine does not set urb->number_of_packets or urb->iso_frame_desc[]. Alan Stern > * > * Note that High Speed and SuperSpeed(+) interrupt endpoints use a logarithmic > * encoding of the endpoint interval, and express polling intervals in >
