hwmon: (max31790) add fanN_enable

The MAX31790 has a tach input enable bit in each fan's configuration
register. This is only enabled by the driver if RPM mode is selected,
but the driver doesn't provide a way to independently enable tachometer
input regardless of the regulator mode.

By adding the fanN_enable sysfs files, we can decouple the tach input
from the regulator mode. Also update the documentation.
Signed-off-by: Justin Ledford <justinledford@google.com>
Link: https://lore.kernel.org/r/20220829195930.2521755-1-justinledford@google.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/max31790.rst

@@ -38,6 +38,7 @@ Sysfs entries
 fan[1-12]_input    RO  fan tachometer speed in RPM
 fan[1-12]_fault    RO  fan experienced fault
 fan[1-6]_target    RW  desired fan speed in RPM
+fan[1-6]_enable    RW  enable or disable the tachometer input
 pwm[1-6]_enable    RW  regulator mode, 0=disabled (duty cycle=0%), 1=manual mode, 2=rpm mode
 pwm[1-6]           RW  read: current pwm duty cycle,
                        write: target pwm duty cycle (0-255)

drivers/hwmon/max31790.c

@@ -202,6 +202,9 @@ static int max31790_read_fan(struct device *dev, u32 attr, int channel,
 		}
 		mutex_unlock(&data->update_lock);
 		return 0;
+	case hwmon_fan_enable:
+		*val = !!(data->fan_config[channel] & MAX31790_FAN_CFG_TACH_INPUT_EN);
+		return 0;
 	default:
 		return -EOPNOTSUPP;
 	}
@@ -214,7 +217,7 @@ static int max31790_write_fan(struct device *dev, u32 attr, int channel,
 	struct i2c_client *client = data->client;
 	int target_count;
 	int err = 0;
-	u8 bits;
+	u8 bits, fan_config;
 	int sr;
 
 	mutex_lock(&data->update_lock);
@@ -243,6 +246,23 @@ static int max31790_write_fan(struct device *dev, u32 attr, int channel,
 					MAX31790_REG_TARGET_COUNT(channel),
 					data->target_count[channel]);
 		break;
+	case hwmon_fan_enable:
+		fan_config = data->fan_config[channel];
+		if (val == 0) {
+			fan_config &= ~MAX31790_FAN_CFG_TACH_INPUT_EN;
+		} else if (val == 1) {
+			fan_config |= MAX31790_FAN_CFG_TACH_INPUT_EN;
+		} else {
+			err = -EINVAL;
+			break;
+		}
+		if (fan_config != data->fan_config[channel]) {
+			err = i2c_smbus_write_byte_data(client, MAX31790_REG_FAN_CONFIG(channel),
+							fan_config);
+			if (!err)
+				data->fan_config[channel] = fan_config;
+		}
+		break;
 	default:
 		err = -EOPNOTSUPP;
 		break;
@@ -270,6 +290,10 @@ static umode_t max31790_fan_is_visible(const void *_data, u32 attr, int channel)
 		    !(fan_config & MAX31790_FAN_CFG_TACH_INPUT))
 			return 0644;
 		return 0;
+	case hwmon_fan_enable:
+		if (channel < NR_CHANNEL)
+			return 0644;
+		return 0;
 	default:
 		return 0;
 	}
@@ -423,12 +447,12 @@ static umode_t max31790_is_visible(const void *data,
 
 static const struct hwmon_channel_info *max31790_info[] = {
 	HWMON_CHANNEL_INFO(fan,
-			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
-			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
-			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
-			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
-			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
-			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
+			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
+			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
+			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
+			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
+			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
+			   HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
 			   HWMON_F_INPUT | HWMON_F_FAULT,
 			   HWMON_F_INPUT | HWMON_F_FAULT,
 			   HWMON_F_INPUT | HWMON_F_FAULT,