linux-kernel - [PATCH] usb: gadget: dummy: fix nonsensical comparisons

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Date:   Tue,  5 Sep 2017 09:56:55 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Tatyana Brokhman <tlinder@...eaurora.org>,
        Felipe Balbi <balbi@...com>,
        Alan Stern <stern@...land.harvard.edu>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] usb: gadget: dummy: fix nonsensical comparisons

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@...com>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/usb/gadget/udc/dummy_hcd.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/udc/dummy_hcd.c b/drivers/usb/gadget/udc/dummy_hcd.c
index a030d7923d7d..54e8e37d2bc8 100644
--- a/drivers/usb/gadget/udc/dummy_hcd.c
+++ b/drivers/usb/gadget/udc/dummy_hcd.c
@@ -376,10 +376,10 @@ static void set_link_state_by_speed(struct dummy_hcd *dum_hcd)
 				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)
+			     USB_PORT_STAT_ENABLE) == 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 {
-- 
2.9.0