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hwmon: (lm70) Fix rounding of negative temperatures

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temp1_input_show() drops the low bits of the temperature register by
dividing the raw value (raw / 32 on the LM70). These bits are not part
of the temperature: the LM70, LM71, LM74 and TMP122/TMP124 always
return some of them as 1, and the TMP125 fills them with copies of the
temperature LSB. Division rounds toward zero, so a negative temperature
with any of these bits set is reported one LSB too high.

For example, the TMP122 returns 0xffff for -0.0625 degrees C, which the
driver reports as 0. The LM70 returns 0xf39f for -25 degrees C, which
the driver reports as -24750.

Use an arithmetic right shift instead, which drops the low bits and
rounds down.

Fixes: e1a8e913f9 ("[PATCH] lm70: New hardware monitoring driver")
Fixes: a86e94dc94 ("hwmon: (lm70) Add support for LM71 and LM74")
Fixes: cd929672a9 ("hwmon: (lm70) Add ti,tmp125 support")
Cc: stable@vger.kernel.org
Signed-off-by: Ridham Khurana <khurana.ridham222@gmail.com>
Link: https://patch.msgid.link/20260924205326.1739229-1-khurana.ridham222@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Ridham Khurana 2026-09-24 20:53:23 +00:00 committed by Guenter Roeck
parent f58c16056f
commit eddb0aaacc
1 changed files with 4 additions and 4 deletions
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8
drivers/hwmon/lm70.c
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@ -96,21 +96,21 @@ static ssize_t temp1_input_show(struct device *dev,
*/
switch (p_lm70->chip) {
case LM70_CHIP_LM70:
val = ((int)raw / 32) * 250;
val = ((int)raw >> 5) * 250;
break;
case LM70_CHIP_TMP121:
case LM70_CHIP_TMP122:
case LM70_CHIP_LM74:
val = ((int)raw / 8) * 625 / 10;
val = ((int)raw >> 3) * 625 / 10;
break;
case LM70_CHIP_LM71:
val = ((int)raw / 4) * 3125 / 100;
val = ((int)raw >> 2) * 3125 / 100;
break;
case LM70_CHIP_TMP125:
val = (sign_extend32(raw, 14) / 32) * 250;
val = (sign_extend32(raw, 14) >> 5) * 250;
break;
}