On Tue, 30 Jul 2013, Alan Stern wrote:
> I can try to ameliorate the situation. Although the 7-ms delay will
> inevitably cause an underrun, it doesn't have to cause errors the way
> it does now. I'll write a patch to handle this. It may take a few
> days.
James, see what happens with this patch. It will print a warning
message in the system log every time it detects an underrun, but it
won't cause an URB submission failure any more.
Alan Stern
Index: usb-3.11/drivers/usb/host/ehci-sched.c
===================================================================
--- usb-3.11.orig/drivers/usb/host/ehci-sched.c
+++ usb-3.11/drivers/usb/host/ehci-sched.c
@@ -1391,21 +1391,20 @@ iso_stream_schedule (
/* Behind the scheduling threshold? */
if (unlikely(start < next)) {
+ unsigned now2 = (now - base) & (mod - 1);
/* USB_ISO_ASAP: Round up to the first available slot */
if (urb->transfer_flags & URB_ISO_ASAP)
start += (next - start + period - 1) & -period;
/*
- * Not ASAP: Use the next slot in the stream. If
- * the entire URB falls before the threshold, fail.
+ * Not ASAP: Use the next slot in the stream,
+ * no matter what.
*/
- else if (start + span - period < next) {
- ehci_dbg(ehci, "iso urb late %p (%u+%u < %u)\n",
+ else if (start + span - period < now2) {
+ ehci_warn(ehci, "iso underrun %p (%u+%u < %u)\n",
urb, start + base,
- span - period, next + base);
- status = -EXDEV;
- goto fail;
+ span - period, now2 + base);
}
}
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