patch "usb: gadget: f_fs: Only return delayed status when len is 0" added to usb-linus

This is a note to let you know that I've just added the patch titled

usb: gadget: f_fs: Only return delayed status when len is 0

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Jerry Zhang <[email protected]>
Date: Mon, 2 Jul 2018 12:48:08 -0700
Subject: usb: gadget: f_fs: Only return delayed status when len is 0

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.

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

index 33e2030503fa..3ada83d81bda 100644
@@ -3263,7 +3263,7 @@ static int ffs_func_setup(struct usb_function *f,
 	__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 bool ffs_func_req_match(struct usb_function *f,

2.18.0