Re: [PATCH] usb: gadget: function: acm: return zlp for OUT setup

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On Wed, 14 Oct 2015, Jassi Brar wrote:

> BTW, should the gadget stack ever queue a Non-ZLP as reply to some
> setup request that has USB_DIR_IN not set?

Yes.  If USB_DIR_IN is not set then the control transfer is OUT, so the
gadget needs to queue a request to receive some data from the host.  
That request will obviously need to be a non-ZLP.  In fact, it's hard
to think of a situation where a gadget would ever want to submit a
zero-length OUT request.  Isn't the UDC driver supposed to handle the
status stage of a control-IN transfer automatically?

Could this cause the problem you're seeing?  The host tries to send 
more data than the gadget is ready to receive?  (Although then the 
error code on the gadget side should be -75, not -71.)

Alan Stern

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