hwmon: (ina2xx) Cast to s16 on shunt and current regs

All devices supported by ina2xx are bidirectional and report the
measured shunt voltage and power values as a signed 16 bit, but the
current driver implementation caches all registers as u16, leading
to an incorrect sign extension when reporting to userspace in
ina2xx_get_value().

This patch fixes the problem by casting the signed registers to s16.
Tested on an INA219.

Signed-off-by: Fabio Baltieri <fabio.baltieri@gmail.com>
Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/hwmon/ina2xx.c b/drivers/hwmon/ina2xx.c
index 93d26e8af3e2..bfd3f3eeabcd 100644
--- a/drivers/hwmon/ina2xx.c
+++ b/drivers/hwmon/ina2xx.c
@@ -148,7 +148,8 @@ static int ina2xx_get_value(struct ina2xx_data *data, u8 reg)
 
         switch (reg) {
         case INA2XX_SHUNT_VOLTAGE:
-                val = DIV_ROUND_CLOSEST(data->regs[reg],
+                /* signed register */
+                val = DIV_ROUND_CLOSEST((s16)data->regs[reg],
                                         data->config->shunt_div);
                 break;
         case INA2XX_BUS_VOLTAGE:
@@ -160,8 +161,8 @@ static int ina2xx_get_value(struct ina2xx_data *data, u8 reg)
                 val = data->regs[reg] * data->config->power_lsb;
                 break;
         case INA2XX_CURRENT:
-                /* LSB=1mA (selected). Is in mA */
-                val = data->regs[reg];
+                /* signed register, LSB=1mA (selected), in mA */
+                val = (s16)data->regs[reg];
                 break;
         default:
                 /* programmer goofed */