hwmon: (max31790): Support config PWM output becomes TACH

Support the "pwm-to-tach" property to config the PWM outputs to
serve as tachometer inputs.

Signed-off-by: Chanh Nguyen <[email protected]>

Author: chnguyen-ampere

Documentation/devicetree/bindings/hwmon/max31790.txt

@@ -0,0 +1,30 @@
+Bindings for the Maxim MAX31790 Fan Controller
+==========================================================
+
+Reference:
+
+https://datasheets.maximintegrated.com/en/ds/MAX31790.pdf
+
+The MAX31790 controls the speeds of up to six fans
+using six independent PWM outputs. The desired fan
+speeds (or PWM duty cycles) are written through the I2C
+interface.
+
+Required properties:
+- compatible     : Must be "maxim,max31790"
+- reg            : I2C slave address
+- pwm-to-tach    : An array of six integers respond to six pwm channels for
+                   configuring the pwm to tach mode.
+
+                   When set to 0, the associated PWMOUT produces a PWM waveform 
+                   for control of fan speed. When set to 1, PWMOUT becomes a TACH input
+
+                   Without the "pwm-to-tach" properties, by default "pwm-to-tach" is <0 0 0 0 0 0>
+
+Example: Set PWM channel 5-6 become TACH input mode
+
+        fans@20 {
+                compatible = "maxim,max31790";
+                reg = <0x20>;
+                pwm-to-tach = <0 0 0 0 1 1>;
+        };

drivers/hwmon/max31790.c

@@ -13,6 +13,7 @@
 #include <linux/jiffies.h>
 #include <linux/module.h>
 #include <linux/slab.h>
+#include <linux/property.h>
 
 /* MAX31790 registers */
 #define MAX31790_REG_GLOBAL_CONFIG	0x00
@@ -65,6 +66,7 @@ struct max31790_data {
 	u16 tach[NR_CHANNEL * 2];
 	u16 pwm[NR_CHANNEL];
 	u16 target_count[NR_CHANNEL];
+	u32 mode[NR_CHANNEL];
 };
 
 static struct max31790_data *max31790_update_device(struct device *dev)
@@ -96,7 +98,6 @@ static struct max31790_data *max31790_update_device(struct device *dev)
 			if (rv < 0)
 				goto abort;
 			data->tach[i] = rv;
-
 			if (data->fan_config[i]
 			    & MAX31790_FAN_CFG_TACH_INPUT) {
 				rv = i2c_smbus_read_word_swapped(client,
@@ -490,6 +491,13 @@ static int max31790_init_client(struct i2c_client *client,
 				MAX31790_REG_FAN_CONFIG(i));
 		if (rv < 0)
 			return rv;
+
+		if (data->mode[i]) {
+			rv |= MAX31790_FAN_CFG_TACH_INPUT;
+		} else {
+			rv &= ~(MAX31790_FAN_CFG_TACH_INPUT);
+		}
+
 		data->fan_config[i] = rv;
 
 		rv = i2c_smbus_read_byte_data(client,
@@ -509,6 +517,7 @@ static int max31790_probe(struct i2c_client *client)
 	struct max31790_data *data;
 	struct device *hwmon_dev;
 	int err;
+	int i;
 
 	if (!i2c_check_functionality(adapter,
 			I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA))
@@ -521,6 +530,16 @@ static int max31790_probe(struct i2c_client *client)
 	data->client = client;
 	mutex_init(&data->update_lock);
 
+	if (device_property_present(dev,"pwm-to-tach")) {
+		err = device_property_read_u32_array(dev,"pwm-to-tach",data->mode,NR_CHANNEL);
+		if (err < 0)
+			return err;
+	} else {
+		for (i = 0; i < NR_CHANNEL; i++) {
+			data->mode[i]=0;
+		}
+	}
+
 	/*
 	 * Initialize the max31790 chip
 	 */