[PATCH 1/2] hwmon: (dell-smm) Clamp the pwm value before scaling it

[Rosen Penev <rosenp@gmail.com>]

dell_smm_write() scales the value written to pwmN with

	DIV_ROUND_CLOSEST(val, data->i8k_pwm_mult)

before clamping the result to the valid fan states. The rounding adds
i8k_pwm_mult / 2 to val first, which overflows for values near
LONG_MAX and wraps to a large negative number. That is then clamped to
0, so writing a huge value turns the fan off instead of running it at
the highest speed. With the default fan_max of 2, writing any value
from LONG_MAX - 63 up to LONG_MAX selects fan state 0.

Clamp val to the pwm range of 0 to 255 first.

Fixes: e7f5f275c62a ("i8k: Implement hwmon based fan speed control")
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/hwmon/dell-smm-hwmon.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
index 5ec487843faa..e8b4e8a29e8b 100644
--- a/drivers/hwmon/dell-smm-hwmon.c
+++ b/drivers/hwmon/dell-smm-hwmon.c
@@ -1030,6 +1030,7 @@ static int dell_smm_write(struct device *dev, enum hwmon_sensor_types type, u32
 	case hwmon_pwm:
 		switch (attr) {
 		case hwmon_pwm_input:
+			val = clamp_val(val, 0, 255);
 			pwm = clamp_val(DIV_ROUND_CLOSEST(val, data->i8k_pwm_mult), 0,
 					data->i8k_fan_max);
 
-- 
2.56.0