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hwmon: (max6621) fix negative temperature offset and crit readings

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max6621_read() reads the CONFIG2 offset and the critical alert threshold
registers into a u32 and scales them without sign extension:

	/* offset */ *val = (regval >> MAX6621_REG_TEMP_SHIFT) * 1000L;
	/* crit   */ *val = regval * 1000L;

Both attributes are writable and their write paths clamp to a negative
minimum and encode negative values, so a value written as negative is read
back as a large positive number. For example, writing a -10 degrees C
offset stores max6621_temp_mc2reg(-10000) = (-10 << 6) = 0xfd80; the read
then computes 0xfd80 >> 6 = 1014 -> 1014000 instead of -10000.

Cast the register value to s16 before scaling so the read preserves the
sign the write path encodes. The temperature input path already uses an s8
intermediate and is left unchanged.

Fixes: 92b64580f1 ("hwmon: (max6621) Add support for Maxim MAX6621 temperature sensor")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4
Signed-off-by: Cong Nguyen <congnt264@gmail.com>
Link: https://lore.kernel.org/r/ad0baddbd6163cf73545c8e9273258136718585c.1786334038.git.congnt264@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Cong Nguyen
2026-08-10 11:28:39 +07:00
committed by Guenter Roeck
parent 24fbeb83d9
commit acc52bd431
1 changed files with 2 additions and 2 deletions
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4
drivers/hwmon/max6621.c
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@@ -239,7 +239,7 @@ max6621_read(struct device *dev, enum hwmon_sensor_types type, u32 attr,
if (ret)
return ret;
*val = (regval >> MAX6621_REG_TEMP_SHIFT) *
*val = ((s16)regval >> MAX6621_REG_TEMP_SHIFT) *
1000L;
break;
@@ -254,7 +254,7 @@ max6621_read(struct device *dev, enum hwmon_sensor_types type, u32 attr,
if (ret)
return ret;
*val = regval * 1000L;
*val = (s16)regval * 1000L;
break;
case hwmon_temp_crit_alarm: