Messages in this thread | | | Date | Sat, 6 Sep 2008 16:27:17 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH] USB: g_file_storage: fix handling zero-length packet |
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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<sangsu@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
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