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: f07f9d2467f4 ("hwmon: (tmp513) Use SI constants from units.h")
Fixes: 59dfa75e5d82 ("hwmon: Add driver for Texas Instruments TMP512/513 sensor chips.")
Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
---
drivers/hwmon/tmp513.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/hwmon/tmp513.c b/drivers/hwmon/tmp513.c
index 1c2cb12071b80866b751b71bf39292580cd47929..1c7601de47d0720352d729e35a5b7eeaf109355f 100644
--- a/drivers/hwmon/tmp513.c
+++ b/drivers/hwmon/tmp513.c
@@ -207,7 +207,9 @@ 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 +225,7 @@ 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 +265,8 @@ 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;
---
base-commit: dab2734f8e9ecba609d66d1dd087a392a7774c04
change-id: 20250114-fix-si-prefix-macro-sign-bugs-307673e6ea45
Best regards,
--
David Lechner <dlechner@xxxxxxxxxxxx>
