On Wed, 7 Mar 2007, Pandita, Vikram wrote:
> Alan
> If the peripheral driver is to decide to send a ZLP or not based on the
> length of data transfer, then the API given to Gadget driver of req.zero
> is redundant.
Yes, it is redundant. That doesn't mean it is bad. Lots of little
optimizations are redundant, and this is one of them.
For example, consider that (++x) means the same thing as (x += 1). So
prefix ++ is redundant. That doesn't make it bad.
> My understanding is that the Gadget driver should respect the API and
> set the req.zero responsibly and hence the following fix suggested in
> Gadget Zero. Else the zero flag can be removed?
I don't know what you mean by "responsibly". The gadget driver can set
req.zero whenever it wants to. The peripheral controller driver then has
to send an extra zero-length packet if and only if req.length is > 0 and
is an exact multiple of the maxpacket size. What's wrong with that?
> Signed-off-by: Vikram Pandita <[EMAIL PROTECTED]>
> ---
> diff -purN a/drivers/usb/gadget/zero.c b/drivers/usb/gadget/zero.c
> --- 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);
This patch is bad. It adds extra code for no reason.
If you think the "zero" flag should be removed, try re-writing this
routine without it. You will have to add an awful lot of additional code.
Alan Stern
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