[RFT PATCH 3/3] hwmon: (nct6775) Fix tolerance bitmask when reading REG_FAN_MODE

[Guenter Roeck <linux@roeck-us.net>]

On NCT6775, bits 0..3 of REG_FAN_MODE hold the temperature or fan speed
tolerance (tolerance_mask is 0x0f), whereas on NCT5525, NCT6106,
NCT6116, NCT6126, and NCT6776+, only bits 0..2 hold the temperature
tolerance or low 3 bits of speed tolerance (tolerance_mask is 0x07).
However, nct6775_update_pwm() masks fanmodecfg with a hardcoded 0x0f.

When bit 3 of REG_FAN_MODE is set on chips where tolerance_mask is 0x07,
nct6775_update_pwm() includes bit 3 in temp_tolerance[0] and
target_speed_tolerance, corrupting reported tolerance values and causing
pwm_update_registers() to OR bit 3 back into REG_FAN_MODE.

Mask fanmodecfg with data->tolerance_mask instead of 0x0f in
nct6775_update_pwm().

Fixes: cdcaeceb74ff ("hwmon: (nct6775) Add support for automatic fan control")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://sashiko.dev
Cc: Anton Lundin <glance@ac2.se>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/nct6775-core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/nct6775-core.c b/drivers/hwmon/nct6775-core.c
index 1d63747a2f38..ff7f7468185d 100644
--- a/drivers/hwmon/nct6775-core.c
+++ b/drivers/hwmon/nct6775-core.c
@@ -1510,10 +1510,10 @@ static int nct6775_update_pwm(struct device *dev)
 
 		if (!data->temp_tolerance[0][i] ||
 		    data->pwm_enable[i] != speed_cruise)
-			data->temp_tolerance[0][i] = fanmodecfg & 0x0f;
+			data->temp_tolerance[0][i] = fanmodecfg & data->tolerance_mask;
 		if (!data->target_speed_tolerance[i] ||
 		    data->pwm_enable[i] == speed_cruise) {
-			u8 t = fanmodecfg & 0x0f;
+			u8 t = fanmodecfg & data->tolerance_mask;
 
 			if (data->REG_TOLERANCE_H) {
 				err = nct6775_read_value(data, data->REG_TOLERANCE_H[i], &reg);
-- 
2.45.2