Messages in this thread | | | Date | Thu, 11 Aug 2011 02:57:41 +0200 | Subject | Re: Allocating buffers for USB transfers (again) | From | Daniel Mack <> |
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On Thu, Aug 11, 2011 at 1:15 AM, Sarah Sharp <sarah.a.sharp@linux.intel.com> wrote: > On Wed, Aug 10, 2011 at 05:33:02PM +0200, Daniel Mack wrote: >> On 08/10/2011 04:32 PM, Alan Stern wrote: >> >Looking at the driver's current code, it appears that your patch >> >does not fix the bug properly. Using discontiguous regions in the >> >transfer buffer is perfectly okay. The real problem is later on, >> >where you do: >> > >> >if (send_it) { out->number_of_packets = FRAMES_PER_URB; >> > >> >This should be >> > >> >out->number_of_packets = outframe; >> > >> >The way it is now, the USB stack will try to use data from all the >> >frame descriptors, and the last few will be stale because the loop >> >doesn't set them. >> >> That's actually true, even though it doesn't seem to cause any trouble. >> I tested everything here of course, and the output URBs return back from >> the USB stack with their length fields zeroed out, which then >> causes the stack to send packets with zero-length fields at the end. > > Actually, it causes system hangs when the driver is loaded on a device > attached to a USB 3.0 port, as Alan Stern pointed out: > > https://bugzilla.kernel.org/show_bug.cgi?id=40702
Yes, I've noticed this.
> Please don't submit zero-length transfers. The xHCI driver just isn't > able to handle it. Arguably, it probably should have just rejected your > URB when it found a zero length buffer, so I'll probably be submitting a > patch to fix that.
According to the spec, sending zero-length frames should be fine, no? Is there any particular reason why XCHI can't handle this while EHCI can? And does my patch fix the driver for XHCI?
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