linux-kernel - [PATCH 4.2.y-ckt 032/305] stmmac: avoid ipq806x constant overflow warning

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Message-Id: <1452902519-2754-33-git-send-email-kamal@canonical.com>
Date:	Fri, 15 Jan 2016 15:57:26 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Arnd Bergmann <arnd@...db.de>,
	"David S. Miller" <davem@...emloft.net>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 032/305] stmmac: avoid ipq806x constant overflow warning

4.2.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

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

commit 49e4a2293035b420e807e739999d59c8ec1488e9 upstream.

Building dwmac-ipq806x on a 64-bit architecture produces a harmless
warning from gcc:

stmmac/dwmac-ipq806x.c: In function 'ipq806x_gmac_probe':
include/linux/bitops.h:6:19: warning: overflow in implicit constant conversion [-Woverflow]
  val = QSGMII_PHY_CDR_EN |
stmmac/dwmac-ipq806x.c:333:8: note: in expansion of macro 'QSGMII_PHY_CDR_EN'
 #define QSGMII_PHY_CDR_EN   BIT(0)
 #define BIT(nr)   (1UL << (nr))

This is a result of the type conversion rules in C, when we take the
logical OR of multiple different types. In particular, we have
and unsigned long

	QSGMII_PHY_CDR_EN == BIT(0) == (1ul << 0) == 0x0000000000000001ul

and a signed int

	0xC << QSGMII_PHY_TX_DRV_AMP_OFFSET == 0xc0000000

which together gives a signed long value

	0xffffffffc0000001l

and when this is passed into a function that takes an unsigned int type,
gcc warns about the signed overflow and the loss of the upper 32-bits that
are all ones.

This patch adds 'ul' type modifiers to the literal numbers passed in
here, so now the expression remains an 'unsigned long' with the upper
bits all zero, and that avoids the signed overflow and the warning.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Fixes: b1c17215d718 ("stmmac: add ipq806x glue layer")
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.c
index f0e4bb4..ae551f4 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.c
@@ -320,11 +320,11 @@ static void *ipq806x_gmac_setup(struct platform_device *pdev)
 			     QSGMII_PHY_RX_SIGNAL_DETECT_EN |
 			     QSGMII_PHY_TX_DRIVER_EN |
 			     QSGMII_PHY_QSGMII_EN |
-			     0x4 << QSGMII_PHY_PHASE_LOOP_GAIN_OFFSET |
-			     0x3 << QSGMII_PHY_RX_DC_BIAS_OFFSET |
-			     0x1 << QSGMII_PHY_RX_INPUT_EQU_OFFSET |
-			     0x2 << QSGMII_PHY_CDR_PI_SLEW_OFFSET |
-			     0xC << QSGMII_PHY_TX_DRV_AMP_OFFSET);
+			     0x4ul << QSGMII_PHY_PHASE_LOOP_GAIN_OFFSET |
+			     0x3ul << QSGMII_PHY_RX_DC_BIAS_OFFSET |
+			     0x1ul << QSGMII_PHY_RX_INPUT_EQU_OFFSET |
+			     0x2ul << QSGMII_PHY_CDR_PI_SLEW_OFFSET |
+			     0xCul << QSGMII_PHY_TX_DRV_AMP_OFFSET);
 	}
 
 	return gmac;
-- 
1.9.1