hwmon: (ltc2990) Fix incorrect conversion of negative temperatures

Fix incorrect conversion of negative temperatures by using
sign_extend32() instead of a home-grown conversion function.

Fixes: df922703574e ("hwmon: Add LTC2990 sensor driver")
Signed-off-by: Tom Levens <tom.levens@cern.ch>
[groeck: Updated subject and description]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

1 files changed, 4 insertions, 14 deletions

diff --git a/drivers/hwmon/ltc2990.c b/drivers/hwmon/ltc2990.c
index 8f8fe059ab48..e320d212ac27 100644
--- a/drivers/hwmon/ltc2990.c
+++ b/drivers/hwmon/ltc2990.c
@@ -11,6 +11,7 @@
  * the chip's internal temperature and Vcc power supply voltage.
  */
 
+#include <linux/bitops.h>
 #include <linux/err.h>
 #include <linux/hwmon.h>
 #include <linux/hwmon-sysfs.h>
@@ -34,15 +35,6 @@
 #define LTC2990_CONTROL_MODE_CURRENT    0x06
 #define LTC2990_CONTROL_MODE_VOLTAGE    0x07
 
-/* convert raw register value to sign-extended integer in 16-bit range */
-static int ltc2990_voltage_to_int(int raw)
-{
-        if (raw & BIT(14))
-                return -(0x4000 - (raw & 0x3FFF)) << 2;
-        else
-                return (raw & 0x3FFF) << 2;
-}
-
 /* Return the converted value from the given register in uV or mC */
 static int ltc2990_get_value(struct i2c_client *i2c, u8 reg, int *result)
 {
@@ -55,18 +47,16 @@ static int ltc2990_get_value(struct i2c_client *i2c, u8 reg, int *result)
         switch (reg) {
         case LTC2990_TINT_MSB:
                 /* internal temp, 0.0625 degrees/LSB, 13-bit  */
-                val = (val & 0x1FFF) << 3;
-                *result = (val * 1000) >> 7;
+                *result = sign_extend32(val, 12) * 1000 / 16;
                 break;
         case LTC2990_V1_MSB:
         case LTC2990_V3_MSB:
                  /* Vx-Vy, 19.42uV/LSB. Depends on mode. */
-                *result = ltc2990_voltage_to_int(val) * 1942 / (4 * 100);
+                *result = sign_extend32(val, 14) * 1942 / 100;
                 break;
         case LTC2990_VCC_MSB:
                 /* Vcc, 305.18μV/LSB, 2.5V offset */
-                *result = (ltc2990_voltage_to_int(val) * 30518 /
-                           (4 * 100 * 1000)) + 2500;
+                *result = sign_extend32(val, 14) * 30518 / (100 * 1000) + 2500;
                 break;
         default:
                 return -EINVAL; /* won't happen, keep compiler happy */