On Tue, Jan 14, 2025 at 03:45:52PM -0600, David Lechner wrote:
> 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>
Applied.
Thanks,
Guenter
> ---
> drivers/hwmon/tmp513.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
>
> ---
> base-commit: dab2734f8e9ecba609d66d1dd087a392a7774c04
> change-id: 20250114-fix-si-prefix-macro-sign-bugs-307673e6ea45
>
> Best regards,
>
> 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;
