On Sat, 27 Jun 2015, Jayan John wrote: > On Fri, Jun 26, 2015 at 8:44 PM, David Laight <David.Laight@xxxxxxxxxx> wrote: > > 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 > > > > Thanks for the pointers. This is not using the xhci driver. > > - This is a ep0 OUT transfer. Does the host need to add a ZLP for 64 > byte aligned data transfer? I'm not sure what you mean here by "aligned", but in general the answer is No. > - Is it not expected for the completion interrupt be raised on > receiving the 64 bytes of data, irrespective of whether or not a ZLP > has been sent. It is expected. Did you check the wLength value in the Setup packet? Is it equal to 64? Does the hid gadget driver then queue a request for a 64-byte OUT transfer on ep0? If it does then there's a bug in the UDC driver or hardware. 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
