Commit e2c68cea authored by David Lechner's avatar David Lechner Committed by Guenter Roeck
Browse files

hwmon: (tmp513) Fix division of negative numbers 



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: f07f9d24 ("hwmon: (tmp513) Use SI constants from units.h")
Fixes: 59dfa75e ("hwmon: Add driver for Texas Instruments TMP512/513 sensor chips.")
Signed-off-by: default avatarDavid Lechner <dlechner@baylibre.com>
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: default avatarGuenter Roeck <linux@roeck-us.net>
parent 5bc55a33

drivers/hwmon/tmp513.c

+4 −3
Original line number Diff line number Diff line
@@ -207,7 +207,8 @@ 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:
@@ -223,7 +224,7 @@ 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:
@@ -263,7 +264,7 @@ 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;