[PATCH v2] hwmon: (gpd-fan) Reject EC PWM value 0 as invalid

[Pei Xiao]

The EC firmware is expected to return values in [1, pwm_max]. A read of 0
is illegal and would cause underflow in the conversion formula. Explicitly
check for 0 and return -EIO.

Signed-off-by: Pei Xiao <xiaopei01@xxxxxxxxxx>
---
changlogs in v2
1.Use the same comment format as the original driver.
---
 drivers/hwmon/gpd-fan.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/hwmon/gpd-fan.c b/drivers/hwmon/gpd-fan.c
index d1993cd645cb..ed212615b2fe 100644
--- a/drivers/hwmon/gpd-fan.c
+++ b/drivers/hwmon/gpd-fan.c
@@ -341,6 +341,10 @@ static int gpd_wm2_read_pwm(struct gpd_fan_data *data)
 
 	gpd_ecram_read(drvdata, drvdata->pwm_write, &var);
 
+	// EC PWM register valid range is 1 ~ pwm_max; 0 is an invalid state
+	if (unlikely(!var))
+		return -EIO;
+
 	// Match gpd_generic_write_pwm(u8) below
 	return DIV_ROUND_CLOSEST((var - 1) * 255, (drvdata->pwm_max - 1));
 }
-- 
2.25.1