On Mon, Jan 06, 2020 at 11:17:12AM -0500, Alan Stern wrote:
> 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.
I'll catch this when it hits Linus's tree.
thanks,
greg k-h
