usb: gadget: ffs: Let setup() return USB_GADGET_DELAYED_STATUS

[ Upstream commit 946ef68ad4e45aa048a5fb41ce8823ed29da866a ]

Some UDC drivers (like the DWC3) expect that the response to a setup()
request is queued from within the setup function itself so that it is
available as soon as setup() has completed.

Upon receiving a setup request the function fs driver creates an event that
is made available to userspace. And only once userspace has acknowledged
that event the response to the setup request is queued.

So it violates the requirement of those UDC drivers and random failures can
be observed. This is basically a race condition and if userspace is able to
read the event and queue the response fast enough all is good. But if it is
not, for example because other processes are currently scheduled to run,
the USB host that sent the setup request will observe an error.

To avoid this the gadget framework provides the USB_GADGET_DELAYED_STATUS
return code. If a setup() callback returns this value the UDC driver is
aware that response is not yet available and can uses the appropriate
methods to handle this case.

Since in the case of function fs the response will never be available when
the setup() function returns make sure that this status code is used.

This fixed random occasional failures that were previously observed on a
DWC3 based system under high system load.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[dwoo08.lee: cherry-pick linux-4.9.y stable commit 10be2659c629 to stablize f_fs]
Signed-off-by: Dongwoo Lee <dwoo08.lee@samsung.com>
Change-Id: I1b88c4739c9007bfd515b670401035ef2bc541fc

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 7a80456873fe7dc69c987c3168ce3f8dd6a82099..600bd8ed6eccf4a50d1c63fc7436867ee1f2c5f3 100644 (file)
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -3250,7 +3250,7 @@ static int ffs_func_setup(struct usb_function *f,
        __ffs_event_add(ffs, FUNCTIONFS_SETUP);
        spin_unlock_irqrestore(&ffs->ev.waitq.lock, flags);
 
-       return 0;
+       return USB_GADGET_DELAYED_STATUS;
 }
 
 static bool ffs_func_req_match(struct usb_function *f,