hwmon: (isl28022) Fix current reading calculation

According to the ISL28022 datasheet, bit15 of the current register is
representing -32768. Fix the calculation to properly handle this bit,
ensuring correct measurements for negative values.

Signed-off-by: Yikai Tsai <yikai.tsai.wiwynn@gmail.com>
Link: https://lore.kernel.org/r/20250519084055.3787-2-yikai.tsai.wiwynn@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/isl28022.c b/drivers/hwmon/isl28022.c
index 0f27ac556f5162ab8c8148374b306af7ef3156b4..c2e559dde63f6188361f83b0cf736689de92d4db 100644 (file)
--- a/drivers/hwmon/isl28022.c
+++ b/drivers/hwmon/isl28022.c
@@ -154,6 +154,7 @@ static int isl28022_read_current(struct device *dev, u32 attr, long *val)
        struct isl28022_data *data = dev_get_drvdata(dev);
        unsigned int regval;
        int err;
+       u16 sign_bit;
 
        switch (attr) {
        case hwmon_curr_input:
@@ -161,8 +162,9 @@ static int isl28022_read_current(struct device *dev, u32 attr, long *val)
                                  ISL28022_REG_CURRENT, &regval);
                if (err < 0)
                        return err;
-               *val = ((long)regval * 1250L * (long)data->gain) /
-                       (long)data->shunt;
+               sign_bit = (regval >> 15) & 0x01;
+               *val = (((long)(((u16)regval) & 0x7FFF) - (sign_bit * 32768)) *
+                       1250L * (long)data->gain) / (long)data->shunt;
                break;
        default:
                return -EOPNOTSUPP;