[PATCH 4.4 14/23] usb: gadget: f_fs: Only return delayed status when len is 0

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jerry Zhang <zhangjerry@google.com>

commit 4d644abf25698362bd33d17c9ddc8f7122c30f17 upstream.

Commit 1b9ba000 ("Allow function drivers to pause control
transfers") states that USB_GADGET_DELAYED_STATUS is only
supported if data phase is 0 bytes.

It seems that when the length is not 0 bytes, there is no
need to explicitly delay the data stage since the transfer
is not completed until the user responds. However, when the
length is 0, there is no data stage and the transfer is
finished once setup() returns, hence there is a need to
explicitly delay completion.

This manifests as the following bugs:

Prior to 946ef68ad4e4 ('Let setup() return
USB_GADGET_DELAYED_STATUS'), when setup is 0 bytes, ffs
would require user to queue a 0 byte request in order to
clear setup state. However, that 0 byte request was actually
not needed and would hang and cause errors in other setup
requests.

After the above commit, 0 byte setups work since the gadget
now accepts empty queues to ep0 to clear the delay, but all
other setups hang.

Fixes: 946ef68ad4e4 ("Let setup() return USB_GADGET_DELAYED_STATUS")
Signed-off-by: Jerry Zhang <zhangjerry@google.com>
Cc: stable <stable@vger.kernel.org>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/gadget/function/f_fs.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -3037,7 +3037,7 @@ static int ffs_func_setup(struct usb_fun
 	__ffs_event_add(ffs, FUNCTIONFS_SETUP);
 	spin_unlock_irqrestore(&ffs->ev.waitq.lock, flags);
 
-	return USB_GADGET_DELAYED_STATUS;
+	return creq->wLength == 0 ? USB_GADGET_DELAYED_STATUS : 0;
 }
 
 static void ffs_func_suspend(struct usb_function *f)