hwmon: (tmp513) Fix division of negative numbers

[ Upstream commit e2c68ce ]

Fix several issues with division of negative numbers in the tmp513
driver.

The docs on the DIV_ROUND_CLOSEST macro explain that dividing a negative
value by an unsigned type is undefined behavior. The driver was doing
this in several places, i.e. data->shunt_uohms has type of u32. The
actual "undefined" behavior is that it converts both values to unsigned
before doing the division, for example:

    int ret = DIV_ROUND_CLOSEST(-100, 3U);

results in ret == 1431655732 instead of -33.

Furthermore the MILLI macro has a type of unsigned long. Multiplying a
signed long by an unsigned long results in an unsigned long.

So, we need to cast both MILLI and data data->shunt_uohms to long when
using the DIV_ROUND_CLOSEST macro.

Fixes: f07f9d2 ("hwmon: (tmp513) Use SI constants from units.h")
Fixes: 59dfa75 ("hwmon: Add driver for Texas Instruments TMP512/513 sensor chips.")
Signed-off-by: David Lechner <[email protected]>
Link: https://lore.kernel.org/r/20250114-fix-si-prefix-macro-sign-bugs-v1-1-696fd8d10f00@baylibre.com
[groeck: Drop some continuation lines]
Signed-off-by: Guenter Roeck <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
(cherry picked from commit 2f176c0ec9f52cb4b47330cb6958690de08c36ea)
FOF: 0225
Signed-off-by: Brian Maly <[email protected]>

Author: dlech

drivers/hwmon/tmp513.c

@@ -203,7 +203,8 @@ static int tmp51x_get_value(struct tmp51x_data *data, u8 reg, u8 pos,
 		*val = sign_extend32(regval,
 				     reg == TMP51X_SHUNT_CURRENT_RESULT ?
 				     16 - tmp51x_get_pga_shift(data) : 15);
-		*val = DIV_ROUND_CLOSEST(*val * 10 * MILLI, data->shunt_uohms);
+		*val = DIV_ROUND_CLOSEST(*val * 10 * (long)MILLI, (long)data->shunt_uohms);
+
 		break;
 	case TMP51X_BUS_VOLTAGE_RESULT:
 	case TMP51X_BUS_VOLTAGE_H_LIMIT:
@@ -219,7 +220,7 @@ static int tmp51x_get_value(struct tmp51x_data *data, u8 reg, u8 pos,
 	case TMP51X_BUS_CURRENT_RESULT:
 		// Current = (ShuntVoltage * CalibrationRegister) / 4096
 		*val = sign_extend32(regval, 15) * (long)data->curr_lsb_ua;
-		*val = DIV_ROUND_CLOSEST(*val, MILLI);
+		*val = DIV_ROUND_CLOSEST(*val, (long)MILLI);
 		break;
 	case TMP51X_LOCAL_TEMP_RESULT:
 	case TMP51X_REMOTE_TEMP_RESULT_1:
@@ -259,7 +260,7 @@ static int tmp51x_set_value(struct tmp51x_data *data, u8 reg, long val)
 		 * The user enter current value and we convert it to
 		 * voltage. 1lsb = 10uV
 		 */
-		val = DIV_ROUND_CLOSEST(val * data->shunt_uohms, 10 * MILLI);
+		val = DIV_ROUND_CLOSEST(val * (long)data->shunt_uohms, 10 * (long)MILLI);
 		max_val = U16_MAX >> tmp51x_get_pga_shift(data);
 		regval = clamp_val(val, -max_val, max_val);
 		break;