On Mon, 6 Jan 2020, Johan Hovold wrote:
> On Mon, Jan 06, 2020 at 10:43:42AM -0500, Alan Stern wrote:
> > It turns out that even though endpoints with a maxpacket length of 0
> > aren't useful for data transfer, the descriptors do serve other
> > purposes. In particular, skipping them will also skip over other
> > class-specific descriptors for classes such as UVC. This unexpected
> > side effect has caused some UVC cameras to stop working.
> >
> > In addition, the USB spec requires that when isochronous endpoint
> > descriptors are present in an interface's altsetting 0 (which is true
> > on some devices), the maxpacket size _must_ be set to 0. Warning
> > about such things seems like a bad idea.
> >
> > This patch updates an earlier commit which would log a warning and
> > skip these endpoint descriptors. Now we only log a warning, and we
> > don't even do that for isochronous endpoints in altsetting 0.
> >
> > We don't need to worry about preventing endpoints with maxpacket = 0
> > from ever being used for data transfers; usb_submit_urb() already
> > checks for this.
> >
> > Reported-and-tested-by: Roger Whittaker <Roger.Whittaker@xxxxxxxx>
> > Fixes: d482c7bb0541 ("USB: Skip endpoints with 0 maxpacket length")
> > Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> > CC: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> > Link: https://marc.info/?l=linux-usb&m=157790377329882&w=2
>
> Acked-by: Johan Hovold <johan@xxxxxxxxxx>
>
> We also need
>
> Cc: stable <stable@xxxxxxxxxxxxxxx>
>
> as d482c7bb0541 ("USB: Skip endpoints with 0 maxpacket length") ended up
> being (auto- ?) selected for stable.
Absolutely -- I had intended to add that CC: but it slipped my mind
when the email was being prepared.
Alan Stern
