hwmon: (max31790) Detect and report zero fan speed

If a fan is not running or not connected, of if fan monitoring is disabled,
the fan count register returns a fixed value of 0xffe0. So far this is then
translated to a RPM value larger than 0. Since this is misleading and does
not really make much sense, report a fan RPM of 0 in this situation.

Cc: Jan Kundrát <jan.kundrat@cesnet.cz>
Cc: Václav Kubernát <kubernat@cesnet.cz>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/max31790.c b/drivers/hwmon/max31790.c
index 8e4fd9b7c8890f64a88360493e8bc31c63333f45..91fe419b596cd7a0bd4d52fdcbb32111c53d9e37 100644 (file)
--- a/drivers/hwmon/max31790.c
+++ b/drivers/hwmon/max31790.c
@@ -40,6 +40,8 @@
 #define FAN_RPM_MIN                    120
 #define FAN_RPM_MAX                    7864320
 
+#define FAN_COUNT_REG_MAX              0xffe0
+
 #define RPM_FROM_REG(reg, sr)          (((reg) >> 4) ? \
                                         ((60 * (sr) * 8192) / ((reg) >> 4)) : \
                                         FAN_RPM_MAX)
@@ -175,7 +177,10 @@ static int max31790_read_fan(struct device *dev, u32 attr, int channel,
                return 0;
        case hwmon_fan_input:
                sr = get_tach_period(data->fan_dynamics[channel % NR_CHANNEL]);
-               rpm = RPM_FROM_REG(data->tach[channel], sr);
+               if (data->tach[channel] == FAN_COUNT_REG_MAX)
+                       rpm = 0;
+               else
+                       rpm = RPM_FROM_REG(data->tach[channel], sr);
                *val = rpm;
                return 0;
        case hwmon_fan_target: