hwmon: (tmp513) Fix Current Register value interpretation

The value returned by the driver after processing the contents of the
Current Register does not correspond to the TMP512/TMP513 specifications.
A raw register value is converted to a signed integer value by a sign
extension in accordance with the algorithm provided in the specification,
but due to the off-by-one error in the sign bit index, the result is
incorrect. Moreover, negative values will be reported as large positive
due to missing sign extension from u32 to long.

According to the TMP512 and TMP513 datasheets, the Current Register (07h)
is a 16-bit two's complement integer value. E.g., if regval = 1000 0011
0000 0000, then the value must be (-32000 * lsb), but the driver will
return (33536 * lsb).

Fix off-by-one bug, and also cast data->curr_lsb_ua (which is of type u32)
to long to prevent incorrect cast for negative values.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 59dfa75 ("hwmon: Add driver for Texas Instruments TMP512/513 sensor chips.")
Signed-off-by: Murad Masimov <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[groeck: Fixed description line length]
Signed-off-by: Guenter Roeck <[email protected]>

Author: Murad Masimov

drivers/hwmon/tmp513.c

@@ -222,7 +222,7 @@ static int tmp51x_get_value(struct tmp51x_data *data, u8 reg, u8 pos,
 		break;
 	case TMP51X_BUS_CURRENT_RESULT:
 		// Current = (ShuntVoltage * CalibrationRegister) / 4096
-		*val = sign_extend32(regval, 16) * data->curr_lsb_ua;
+		*val = sign_extend32(regval, 15) * (long)data->curr_lsb_ua;
 		*val = DIV_ROUND_CLOSEST(*val, MILLI);
 		break;
 	case TMP51X_LOCAL_TEMP_RESULT: