[PATCH] USB: g_file_storage: fix handling zero-length packet

[sangsu]

According to "CH 5.5.3. Control Transfer Packet Size Constraints",
Zero-length packet should be sent when the last data payload size
is equal to the endpoint's MaxPacketSize. This patch helps
g_file_storage send zero-length packet properly.

This is tested in s3c2440/s5c7329 architectures and works well.

Signed-off-by: SangSu Park<san...@gmail.com>
---
driver/usb/gadget/file_storage.c | 3++-
1 files changed, 2 insertion(+), 1 deletions(-)

--- a/drivers/usb/gadget/file_storage.c 2008-09-01 11:13:03.000000000 -0400
+++ b/drivers/usb/gadget/file_storage.c 2008-09-01 11:16:41.000000000 -0400
@@ -1463,7 +1463,8 @@
if (rc >= 0 && rc != DELAYED_STATUS) {
rc = min(rc, w_length);
fsg->ep0req->length = rc;
- fsg->ep0req->zero = rc < w_length;
+ fsg->ep0req->zero = rc < w_length
+ && (rc % gadget->ep0->maxpacket) == 0;
fsg->ep0req_name = (ctrl->bRequestType & USB_DIR_IN ?
"ep0-in" : "ep0-out");
rc = ep0_queue(fsg);
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[Alan Stern]

On Sat, 6 Sep 2008, sangsu wrote:

> According to "CH 5.5.3. Control Transfer Packet Size Constraints",
> Zero-length packet should be sent when the last data payload size
> is equal to the endpoint's MaxPacketSize.

Not so. 5.5.3 actually says this:

The Data stage of a control transfer from an endpoint to the
host is complete when the endpoint does one of the following:

- Has transferred exactly the amount of data specified during
the Setup stage

- Transfers a packet with a payload size less than
wMaxPacketSize or transfers a zero-length packet

This clearly indicates that if the amount of data specified in the
Setup stage is a multiple of the wMaxPacketSize then there should not
be a zero-length packet, because the transfer ends as soon as the last
wMaxPacketSize packet is sent.

> This patch helps
> g_file_storage send zero-length packet properly.
>
> This is tested in s3c2440/s5c7329 architectures and works well.
>
> Signed-off-by: SangSu Park<san...@gmail.com>
> ---
> driver/usb/gadget/file_storage.c | 3++-
> 1 files changed, 2 insertion(+), 1 deletions(-)
>
> --- a/drivers/usb/gadget/file_storage.c 2008-09-01 11:13:03.000000000 -0400
> +++ b/drivers/usb/gadget/file_storage.c 2008-09-01 11:16:41.000000000 -0400
> @@ -1463,7 +1463,8 @@
> if (rc >= 0 && rc != DELAYED_STATUS) {
> rc = min(rc, w_length);
> fsg->ep0req->length = rc;
> - fsg->ep0req->zero = rc < w_length;
> + fsg->ep0req->zero = rc < w_length
> + && (rc % gadget->ep0->maxpacket) == 0;
> fsg->ep0req_name = (ctrl->bRequestType & USB_DIR_IN ?
> "ep0-in" : "ep0-out");
> rc = ep0_queue(fsg);

Firstly, this patch does not do what your description says it does.

Secondly, the patch is not needed. g_file_storage doesn't have to
check whether the data size is a multiple of MaxPacketSize because the
device controller driver already is supposed to make that check.

Alan Stern