[PATCH 3/3] hwmon: (max31760) Report 0 RPM before the first fan speed measurement

[Stanislav Aleksandrov <lightofmysoul@gmail.com>]

The tachometer count registers initialize to 0 until the first
measurement cycle completes after power-on. To prevent division by
zero, tach_to_rpm() clamped tach == 0 to 1, causing it to compute
and report 3,000,000 RPM (60 * 100000 / 1 / 2).

Return 0 RPM when tach == 0 instead.

Fixes: 38b04ad02d0d ("drivers: hwmon: Add max31760 fan speed controller driver")
Signed-off-by: Stanislav Aleksandrov <lightofmysoul@gmail.com>
---
 drivers/hwmon/max31760.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/max31760.c b/drivers/hwmon/max31760.c
index e967555a21af..896bd0326b8c 100644
--- a/drivers/hwmon/max31760.c
+++ b/drivers/hwmon/max31760.c
@@ -68,8 +68,9 @@ static const int max31760_pwm_freq[] = {33, 150, 1500, 25000};
 
 static int tach_to_rpm(u16 tach)
 {
+	/* The count is 0 until the first measurement */
 	if (tach == 0)
-		tach = 1;
+		return 0;
 
 	return 60 * 100000 / tach / 2;
 }

-- 
2.55.0