dwc_otg: make nak_holdoff work as intended with empty queues #1978
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If URBs reading from non-periodic split endpoints were dequeued and the last transfer from the endpoint was a NAK handshake, the resulting qh->nak_frame value was stale which would result in unnecessarily long polling intervals for the first subsequent transfer with a fresh URB. Fixup qh->nak_frame in dwc_otg_hcd_urb_dequeue and also guard against a case where a single URB is submitted to the endpoint, a NAK was received on the transfer immediately prior to receiving data and the device subsequently resubmits another URB past the qh->nak_frame interval. Fixes raspberrypi#1709
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See #1709. This fixes the lengthy timeout issues seen with the provided test program pair.
The issue with data not being returned immediately after opening a port isn't an issue with dwc_otg: I see usb-serial correctly receiving the data from the HCD therefore the problem is further up the stack.cc @carmarri