[PATCH 6/7] hwmon: (max31790) Detect and report zero fan speed

Guenter Roeck
2021-05-26T15:40:49Z

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>
---
drivers/hwmon/max31790.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/max31790.c b/drivers/hwmon/max31790.c
index 8e4fd9b7c889..91fe419b596c 100644
--- 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:
--
2.25.1