linux-kernel - [PATCH 4.9 045/101] usb: gadget: dummy: fix nonsensical comparisons

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Message-Id: <20181206143014.121988670@linuxfoundation.org>
Date:   Thu,  6 Dec 2018 15:38:44 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Tatyana Brokhman <tlinder@...eaurora.org>,
        Felipe Balbi <balbi@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Arnd Bergmann <arnd@...db.de>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>
Subject: [PATCH 4.9 045/101] usb: gadget: dummy: fix nonsensical comparisons

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

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

From: Arnd Bergmann <arnd@...db.de>

commit 7661ca09b2ff98f48693f431bb01fed62830e433 upstream.

gcc-8 points out two comparisons that are clearly bogus
and almost certainly not what the author intended to write:

drivers/usb/gadget/udc/dummy_hcd.c: In function 'set_link_state_by_speed':
drivers/usb/gadget/udc/dummy_hcd.c:379:31: error: bitwise comparison always evaluates to false [-Werror=tautological-compare]
         USB_PORT_STAT_ENABLE) == 1 &&
                               ^~
drivers/usb/gadget/udc/dummy_hcd.c:381:25: error: bitwise comparison always evaluates to false [-Werror=tautological-compare]
      USB_SS_PORT_LS_U0) == 1 &&
                         ^~

I looked at the code for a bit and came up with a change that makes
it look like what the author probably meant here. This makes it
look reasonable to me and to gcc, shutting up the warning.

It does of course change behavior as the two conditions are actually
evaluated rather than being hardcoded to false, and I have made no
attempt at verifying that the changed logic makes sense in the context
of a USB HCD, so that part needs to be reviewed carefully.

Fixes: 1cd8fd2887e1 ("usb: gadget: dummy_hcd: add SuperSpeed support")
Cc: Tatyana Brokhman <tlinder@...eaurora.org>
Cc: Felipe Balbi <balbi@...nel.org>
Acked-by: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Felipe Balbi <felipe.balbi@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/gadget/udc/dummy_hcd.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/drivers/usb/gadget/udc/dummy_hcd.c
+++ b/drivers/usb/gadget/udc/dummy_hcd.c
@@ -379,11 +379,10 @@ static void set_link_state_by_speed(stru
 			     USB_PORT_STAT_CONNECTION) == 0)
 				dum_hcd->port_status |=
 					(USB_PORT_STAT_C_CONNECTION << 16);
-			if ((dum_hcd->port_status &
-			     USB_PORT_STAT_ENABLE) == 1 &&
-				(dum_hcd->port_status &
-				 USB_SS_PORT_LS_U0) == 1 &&
-				dum_hcd->rh_state != DUMMY_RH_SUSPENDED)
+			if ((dum_hcd->port_status & USB_PORT_STAT_ENABLE) &&
+			    (dum_hcd->port_status &
+			     USB_PORT_STAT_LINK_STATE) == USB_SS_PORT_LS_U0 &&
+			    dum_hcd->rh_state != DUMMY_RH_SUSPENDED)
 				dum_hcd->active = 1;
 		}
 	} else {