On Wed, Jan 15, 2025 at 02:48:27PM -0600, David Lechner wrote:
> Fix use of DIV_ROUND_CLOSEST where a possibly negative value is divided
> by an unsigned type by casting the unsigned type to the signed type of
> the same size (st->r_sense_uohm[channel] has type of u32).
>
> The docs on the DIV_ROUND_CLOSEST macro explain that dividing a negative
> value by an unsigned type is undefined behavior. The actual 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.
>
> Fixes: 2b9ea4262ae9 ("hwmon: Add driver for ltc2991")
> Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
Applied.
Thanks,
Guenter
> ---
> drivers/hwmon/ltc2991.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>
> ---
> base-commit: dab2734f8e9ecba609d66d1dd087a392a7774c04
> change-id: 20250115-hwmon-ltc2991-fix-div-round-closest-c65c05afb881
>
> Best regards,
>
> diff --git a/drivers/hwmon/ltc2991.c b/drivers/hwmon/ltc2991.c
> index 7ca139e4b6aff0b6c3024183e19970b36f927f6e..6d5d4cb846daf3025e55d43cfe311f38bb353621 100644
> --- a/drivers/hwmon/ltc2991.c
> +++ b/drivers/hwmon/ltc2991.c
> @@ -125,7 +125,7 @@ static int ltc2991_get_curr(struct ltc2991_state *st, u32 reg, int channel,
>
> /* Vx-Vy, 19.075uV/LSB */
> *val = DIV_ROUND_CLOSEST(sign_extend32(reg_val, 14) * 19075,
> - st->r_sense_uohm[channel]);
> + (s32)st->r_sense_uohm[channel]);
>
> return 0;
> }
