Re: Gadget Zero patch for ZLP

On Thu, 8 Feb 2007, Pandita, Vikram wrote:

> While sending the string descriptor, Gadget Zero does not send a ZLP in
> case the packet size is maxpacket size, resulting in a USBCV failure. 

Not correct.  Gadget Zero _does_ send a ZLP if the packet size is equal to
the maxpacket size, provided the host requested a longer response.  
Conversely, if the host asked for exactly maxpacket bytes and the gadget
sends back a response of that length, then there should not be a ZLP
added.

> The Ethernet Gadget has the following code which is missing from Gadget
> Zero. Should this be added to the Gadget Zero also?

It isn't needed in either driver, although it doesn't hurt.  The device
controller driver will always check for (value % gadget->ep0->maxpacket)
== 0 before sending the ZLP, so the gadget driver doesn't need to check.

> --- a/drivers/usb/gadget/zero.c	2007-02-02 18:33:34.000000000 +0530
> +++ b/drivers/usb/gadget/zero.c	2007-02-07 17:28:47.000000000 +0530
> @@ -1072,7 +1072,8 @@ unknown:
>  	/* respond with data transfer before status phase? */
>  	if (value >= 0) {
>  		req->length = value;
> -		req->zero = value < w_length;
> +		req->zero = value < w_length &&
> +				(value % gadget->ep0->maxpacket) == 0;
>  		value = usb_ep_queue (gadget->ep0, req, GFP_ATOMIC);
>  		if (value < 0) {
>  			DBG (dev, "ep_queue --> %d\n", value);

Alan Stern


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