Re: uvcvideo failure under xHCI

[Sarah Sharp <sarah.a.sharp@linux.intel.com>]

On Thu, Jun 16, 2011 at 01:39:43PM -0400, Alan Stern wrote:
> On Thu, 16 Jun 2011, Sarah Sharp wrote:
> 
> > > > > Alan, does that seem correct?
> > > 
> > > The description of the behavior of ehci-hcd and uhci-hcd is correct.  
> > > ohci-hcd behaves the same way too.  And they all agree with the 
> > > behavior described in the kerneldoc for struct urb in 
> > > include/linux/usb.h.
> > 
> > Ah, you mean this bit?
> > 
> >  * @status: This is read in non-iso completion functions to get the
> >  *      status of the particular request.  ISO requests only use it
> >  *      to tell whether the URB was unlinked; detailed status for
> >  *      each frame is in the fields of the iso_frame-desc.
> 
> Right.  There's also some more near the end:
> 
>  * Completion Callbacks:
>  *
>  * The completion callback is made in_interrupt(), and one of the first
>  * things that a completion handler should do is check the status field.
>  * The status field is provided for all URBs.  It is used to report
>  * unlinked URBs, and status for all non-ISO transfers.  It should not
>  * be examined before the URB is returned to the completion handler.
> 
> > > Under the circumstances, the documentation file should be changed.  
> > > Sarah, can you do that along with the change to xhci-hcd?
> > 
> > Sure.  It feels like there should be a note about which values
> > isochronous URBs might have in the urb->status field.  The USB core is
> > the only one that would be setting those, so which values would it set?
> > uvcvideo tests for these error codes:
> > 
> >         case -ENOENT:           /* usb_kill_urb() called. */
> >         case -ECONNRESET:       /* usb_unlink_urb() called. */
> >         case -ESHUTDOWN:        /* The endpoint is being disabled. */
> >         case -EPROTO:           /* Device is disconnected (reported by some
> >                                  * host controller). */
> > 
> > Are there any others.
> 
> -EREMOTEIO, in the unlikely event that URB_SHORT_NOT_OK is set, but no
> others.

Are you saying that the USB core will only set -EREMOTEIO for
isochronous URBs?  Or do you mean that in addition to the status values
that uvcvideo checks, the USB core can also set -EREMOTEIO?

> And I wasn't aware of that last one...  Host controller drivers should
> report -ESHUTDOWN to mean the device has been disconnected, not
> -EPROTO.  But usually HCD don't take these events into account when
> determining URB status codes.

The xHCI driver will return -ESHUTDOWN as a status for URBs when the
host controller is dying.

Sarah Sharp