Re: Linux USB file storage gadget with new UDC

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On Tue, 2 Jul 2013, Victor Yeo wrote:

> > This looks like another bug in the UDC driver.  It performs the Status
> > stage of the Set-Config request before the gadget driver has finished
> > carrying out the request.
> >
> > Notice that the USB_REQ_SET_CONFIGURATION case in standard_setup_req()
> > returns DELAYED_STATUS.  As a result, fsg_setup() does not call
> > ep0_queue(), and so usb_ep_queue() doesn't get called.  The UDC driver
> > is not supposed to ACK the Status stage of an OUT control transfer
> > until usb_ep_queue() is called.
> 
> May i verify my understanding of Set-Config request packet flow?
> 
> Host                   Device
> ------Setup Packet---->
> ------Data0 Packet---->
> <-----Ack Packet-----
> 
> ------ In Packet ---->
> <---- Data1 Packet ----
> ----- Ack Packet ----->
> 
> ----- Out Packet ---->
> ----- Data1 Packet ---->
> <---- Ack Packet -----

No, that's not right.  Set-Config has only two stages, Setup and
Status; there is no Data stage.  The flow is:

Host             Device
----- Setup Packet --->		|
----- Data0 Packet ---> 	|== Setup stage
<---- Ack Packet ------		|

----- In Packet ------>		|
<---- Data1 Packet ----		|== Status stage
----- Ack Packet ----->		|


> "ACK the Status stage of an OUT control transfer", is it referring to
> the Third ACK packet? So UDC driver should ACK only after Data1 packet
> is sent via the usb_ep_queue()?

I meant the Data1 packet above.  The UDC driver should not send this
packet until the gadget driver tells it to (by calling usb_ep_queue).  
Until then, it should send NAK in respond to the In packet.

Alan Stern

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