From: Steve Calfee
> Sent: 26 June 2015 15:59
> > On the host (Wandboard iMX6q) the test app opens /dev/hidraw0 and
> > write 64 bytes with report ID (1). The HID device has no Interrupt OUT
> > ep, therefore uses control endpoint ep0 for the 64 bytes transfer to
> > gadget (Wandboard iMX6q) using set_report.
> >
> > The setup phase is OK and the 64 bytes is written to gadget. However
> > the chipidea interrupt (ci_irq()) and resulting udc interrupt
> > (udc_irq()) is invoked. This indicates that the 64 bytes transaction
> > is not completed over ep0 from host to gadget.
> >
> > **this issue is reproducible for all data transfers that aligns on 64 bytes**
> >
> > ~jayan
> >
> Hi Jayan,
>
> This sounds like a Zero Length Transfer issue. This applies to any
> endpoint including EP0.
>
> A ZLT is needed to end any transfer IFF the length is not already
> known by the protocol. So if the hid URB requests say 1024 bytes and
> the gadget only has 64, it must first send the 64 byte maxpacket and
> then send a zero length packet. This way the host knows the transfer
> is complete.
Is this using the xhci driver?
The ZLP sending code used to be broken.
A couple of patches have been submitted but I don't remember one being applied.
David
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