linux-kernel - [PATCH 3.18 028/145] smc91x: avoid self-comparison warning

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Date:   Sun, 16 Apr 2017 12:48:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.18 028/145] smc91x: avoid self-comparison warning

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

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

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

commit e3ebd894f084255fde19116955ba7054858ff5d6 upstream.

The smc91x driver defines a macro that compares its argument to
itself, apparently to get a true result while using its argument
to avoid a warning about unused local variables.

Unfortunately, this triggers a warning with gcc-6, as the comparison
is obviously useless:

drivers/net/ethernet/smsc/smc91x.c: In function 'smc_hardware_send_pkt':
drivers/net/ethernet/smsc/smc91x.c:563:14: error: self-comparison always evaluates to true [-Werror=tautological-compare]
  if (!smc_special_trylock(&lp->lock, flags)) {

This replaces the macro with another one that behaves similarly,
with a cast to (void) to ensure the argument is used, and using
a literal 'true' as its value.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/ethernet/smsc/smc91x.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/ethernet/smsc/smc91x.c
+++ b/drivers/net/ethernet/smsc/smc91x.c
@@ -535,7 +535,7 @@ static inline void  smc_rcv(struct net_d
 #define smc_special_lock(lock, flags)		spin_lock_irqsave(lock, flags)
 #define smc_special_unlock(lock, flags) 	spin_unlock_irqrestore(lock, flags)
 #else
-#define smc_special_trylock(lock, flags)	(flags == flags)
+#define smc_special_trylock(lock, flags)	((void)flags, true)
 #define smc_special_lock(lock, flags)   	do { flags = 0; } while (0)
 #define smc_special_unlock(lock, flags)	do { flags = 0; } while (0)
 #endif