On Thu, 16 Jun 2011, Laurent Pinchart wrote: > Hi Sarah, > > On Thursday 16 June 2011 04:59:57 Sarah Sharp wrote: > > On Wed, Jun 15, 2011 at 06:39:57PM -0700, Sarah Sharp wrote: > > > When I plug in a webcam under an xHCI host controller in 3.0-rc3+ > > > (basically top of Greg's usb-linus branch) with xHCI debugging turned > > > on, the host controller occasionally cannot keep up with the isochronous > > > transfers, and it tells the xHCI driver that it had to "skip" several > > > microframes of transfers. These "Missed Service Intervals" aren't > > > supposed to be fatal errors, just an indication that something was > > > hogging the PCI memory bandwidth. > > > > > > The xHCI driver then sets the URB's status to -EXDEV, to indicate that > > > some of the iso_frame_desc transferred, and sets at least one frame's > > > > > status to -EXDEV: > > ... > > > > > The urb->status causes uvcvideo code in > > > uvc_status.c:uvc_status_complete() to fail with the message: > > > > > > Jun 15 17:37:11 talon kernel: [ 117.987769] uvcvideo: Non-zero status > > > (-18) in video completion handler. > > > > ... > > > > > I've grepped through drivers/media/video, and it seems like none of the > > > drivers handle the -EXDEV status. What should the xHCI driver be > > > setting the URB's status and frame status to when the xHCI host > > > controller skips over transfers? -EREMOTEIO? > > > > > > Or does it need to set the URB's status to zero, but only set the > > > individual frame status to -EXDEV? > > > > Ok, looking at both EHCI and UHCI, they seem to set the urb->status to > > zero, regardless of what they set the frame descriptor field to. > > > > 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. > According to Documentation/usb/error-codes.txt, host controller drivers should > set the status to -EXDEV. However, no device drivers seem to handle that, > probably because the EHCI/UHCI drivers don't use that error code. > > Drivers are clearly out of sync with the documentation, so we should fix one > of them. Under the circumstances, the documentation file should be changed. Sarah, can you do that along with the change to xhci-hcd? Alan Stern -- 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
