On Mon, Jun 29, 2015 at 7:16 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 29 Jun 2015, Peter Chen wrote: > >> Just like Steve pointed, it should be a ZLT problem, do you have >> below patch in your tree, and the host may not send zlt, but you >> may queue an zero-length request, the f_hid does not set req->zero >> flag either. >> >> commit 953c66469735aed8d2ada639a72b150f01dae605 >> Author: Abbas Raza <Abbas_Raza@xxxxxxxxxx> >> Date: Thu Jul 17 19:34:31 2014 +0800 >> >> usb: chipidea: udc: Disable auto ZLP generation on ep0 >> >> >> If it still has problem, send me apps if possible (with needed kernel >> patches). > > Note that a UDC should _never_ queue an extra zero-length packet for an > OUT transfer, no matter how req->zero is set. In other words, > req->zero is supposed to affect only IN transfers. > Yes UDC gadgets receive packets sent by the host on OUT transfers. If ZLT transfers are needed for the protocol, a short transfer is needed to end an OUT sequence and it must be sent by the sender, in this case the host. The UDC should detect receiving a zero length EP0 OUT and that signals the end of the 64 byte transfer from host to gadget. Regards, Steve -- 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
