| Message ID | 20250115-hwmon-ltc2991-fix-div-round-closest-v1-1-b4929667e457@baylibre.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | hwmon: (ltc2991) Fix mixed signed/unsigned in DIV_ROUND_CLOSEST | expand |
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@baylibre.com> 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; > }
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; }
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@baylibre.com> --- 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,