linux-kernel - Re: ADT746X: logical-bitwise & confusion in set_max_duty_at

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Message-ID: <47D5068F.8050709@tiscali.nl>
Date:	Mon, 10 Mar 2008 10:59:43 +0100
From:	Roel Kluin <12o3l@...cali.nl>
To:	Segher Boessenkool <segher@...nel.crashing.org>
CC:	benh@...nel.crashing.org, linuxppc-dev@...abs.org,
	lkml <linux-kernel@...r.kernel.org>,
	Colin Leroy <colin@...ino.net>,
	"Darrick J. Wong" <djwong@...ibm.com>
Subject: Re: ADT746X: logical-bitwise & confusion in set_max_duty_at_crit()

Segher Boessenkool wrote:
>> diff --git a/drivers/hwmon/adt7473.c b/drivers/hwmon/adt7473.c
>> index 9587869..8ea7da2 100644
>> --- a/drivers/hwmon/adt7473.c
>> +++ b/drivers/hwmon/adt7473.c
>> @@ -570,7 +570,7 @@ static ssize_t set_max_duty_at_crit(struct device
>> *dev,
>>      struct i2c_client *client = to_i2c_client(dev);
>>      struct adt7473_data *data = i2c_get_clientdata(client);
>>      int temp = simple_strtol(buf, NULL, 10);
>> -    temp = temp && 0xFF;
>> +    temp &= 0xFF;
>>
>>      mutex_lock(&data->lock);
>>      data->max_duty_at_overheat = temp;
> 
> The & 0xff here is bogus anyway; temp is only ever used as an u8,
> so just declare it as that, or do proper overflow/underflow checking
> on it.  The patch will need testing on hardware too, since it changes
> behaviour (it should be a bugfix, but who knows).

Maybe someone can test this?
---
logical-bitwise & confusion

Signed-off-by: Roel Kluin <12o3l@...cali.nl>
---
diff --git a/drivers/hwmon/adt7473.c b/drivers/hwmon/adt7473.c
index 9587869..2a2de73 100644
--- a/drivers/hwmon/adt7473.c
+++ b/drivers/hwmon/adt7473.c
@@ -566,11 +566,11 @@ static ssize_t set_max_duty_at_crit(struct device *dev,
 				    const char *buf,
 				    size_t count)
 {
-	u8 reg;
+	u8 reg, temp;
 	struct i2c_client *client = to_i2c_client(dev);
 	struct adt7473_data *data = i2c_get_clientdata(client);
-	int temp = simple_strtol(buf, NULL, 10);
-	temp = temp && 0xFF;
+
+	temp = simple_strtol(buf, NULL, 10) & 0xFF;
 
 	mutex_lock(&data->lock);
 	data->max_duty_at_overheat = temp;

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