linux-kernel - [PATCH] ARM: pxa: fix GPIO double shifts

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Message-Id: <1468657429-13117-1-git-send-email-robert.jarzmik@free.fr>
Date:	Sat, 16 Jul 2016 10:23:49 +0200
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Daniel Mack <daniel@...que.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Russell King <linux@...linux.org.uk>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Dan Carpenter <dan.carpenter@...cle.com>
Subject: [PATCH] ARM: pxa: fix GPIO double shifts

The commit 9bf448c66d4b ("ARM: pxa: use generic gpio operation instead of
gpio register") from Oct 17, 2011, leads to the following static checker
warning:
  arch/arm/mach-pxa/spitz_pm.c:172 spitz_charger_wakeup()
  warn: double left shift '!gpio_get_value(SPITZ_GPIO_KEY_INT)
        << (1 << ((SPITZ_GPIO_KEY_INT) & 31))'

As Dan reported, the value is shifted three times :
 - once by gpio_get_value(), which returns either 0 or BIT(gpio)
 - once by the shift operation '<<'
 - a last time by GPIO_bit(gpio) which is BIT(gpio)

Therefore the calculation lead to a chained or operator of :
 - (1 << gpio) << (1 << gpio) = (2^gpio)^gpio = 2 ^ (gpio * gpio)

It is be sheer luck the former statement works, only because each gpio
used is strictly smaller than 6, and therefore 2^(gpio^2) never
overflows a 32 bits value, and because it is used as a boolean value to
check a gpio activation.

Fixes: 9bf448c66d4b ("ARM: pxa: use generic gpio operation instead of
gpio register")
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Robert Jarzmik <robert.jarzmik@...e.fr>
---
 arch/arm/mach-pxa/corgi_pm.c | 8 +++-----
 arch/arm/mach-pxa/spitz_pm.c | 5 ++---
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/arm/mach-pxa/corgi_pm.c b/arch/arm/mach-pxa/corgi_pm.c
index d9206811be9b..a7bc7e18158e 100644
--- a/arch/arm/mach-pxa/corgi_pm.c
+++ b/arch/arm/mach-pxa/corgi_pm.c
@@ -135,11 +135,9 @@ static unsigned long corgi_charger_wakeup(void)
 {
 	unsigned long ret;
 
-	ret = (!gpio_get_value(CORGI_GPIO_AC_IN) << GPIO_bit(CORGI_GPIO_AC_IN))
-		| (!gpio_get_value(CORGI_GPIO_KEY_INT)
-		<< GPIO_bit(CORGI_GPIO_KEY_INT))
-		| (!gpio_get_value(CORGI_GPIO_WAKEUP)
-		<< GPIO_bit(CORGI_GPIO_WAKEUP));
+	ret = !gpio_get_value(CORGI_GPIO_AC_IN)
+		| !gpio_get_value(CORGI_GPIO_KEY_INT)
+		| !gpio_get_value(CORGI_GPIO_WAKEUP);
 	return ret;
 }
 
diff --git a/arch/arm/mach-pxa/spitz_pm.c b/arch/arm/mach-pxa/spitz_pm.c
index ea9f9034cb54..5a4c45b5a526 100644
--- a/arch/arm/mach-pxa/spitz_pm.c
+++ b/arch/arm/mach-pxa/spitz_pm.c
@@ -168,9 +168,8 @@ static int spitz_should_wakeup(unsigned int resume_on_alarm)
 static unsigned long spitz_charger_wakeup(void)
 {
 	unsigned long ret;
-	ret = ((!gpio_get_value(SPITZ_GPIO_KEY_INT)
-		<< GPIO_bit(SPITZ_GPIO_KEY_INT))
-		| gpio_get_value(SPITZ_GPIO_SYNC));
+	ret = !gpio_get_value(SPITZ_GPIO_KEY_INT)
+		| gpio_get_value(SPITZ_GPIO_SYNC);
 	return ret;
 }
 
-- 
2.1.4