[PATCH] hwmon: max31790: support to config PWM as TACH

[Delphine CC Chiu <Delphine_CC_Chiu@wiwynn.com>]

The PWM outputs of max31790 could be used as tachometer inputs by
setting the fan configuration register, but the driver doesn't support
to config the PWM outputs as tachometer inputs currently.

Add a function to get properties of the setting of max31790 to config
PWM outputs as tachometer inputs before initializing max31790.
For example: set `pwm-as-tach = /bits/ 8 <2 5>` in DTS for max31790 and
the driver will config PWMOUT2 and PWMOUT5 as TACH8 and TACH11.

Signed-off-by: Delphine CC Chiu <Delphine_CC_Chiu@wiwynn.com>
---
 drivers/hwmon/max31790.c | 50 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/drivers/hwmon/max31790.c b/drivers/hwmon/max31790.c
index 0cd44c1e998a..0f8fe911539b 100644
--- a/drivers/hwmon/max31790.c
+++ b/drivers/hwmon/max31790.c
@@ -480,6 +480,52 @@ static const struct hwmon_chip_info max31790_chip_info = {
 	.info = max31790_info,
 };
 
+static int max31790_config_pwm_as_tach(struct device *dev,
+				       struct i2c_client *client)
+{
+	struct device_node *np = dev->of_node;
+	int i, ret = 0, size, channel;
+	u8 pwm_index[NR_CHANNEL] = { 0 };
+	u8 fan_config;
+
+	size = of_property_count_u8_elems(np, "pwm-as-tach");
+
+	if ((size > 0) && (size <= NR_CHANNEL)) {
+		ret = of_property_read_u8_array(np, "pwm-as-tach", pwm_index,
+						size);
+		if (ret) {
+			dev_err(dev,
+				"Property 'pwm-as-tach' cannot be read.\n");
+			return ret;
+		}
+
+		for (i = 0; i < size; i++) {
+			if ((pwm_index[i] == 0) ||
+			    (pwm_index[i] > NR_CHANNEL)) {
+				continue;
+			}
+
+			channel = pwm_index[i] - 1;
+			fan_config = i2c_smbus_read_byte_data(
+				client, MAX31790_REG_FAN_CONFIG(channel));
+			if (fan_config < 0) {
+				dev_err(dev,
+					"Read fan config for channel %d failed.\n",
+					channel);
+				return fan_config;
+			}
+
+			fan_config |= (MAX31790_FAN_CFG_CTRL_MON |
+				       MAX31790_FAN_CFG_TACH_INPUT);
+			i2c_smbus_write_byte_data(
+				client, MAX31790_REG_FAN_CONFIG(channel),
+				fan_config);
+		}
+	}
+
+	return 0;
+}
+
 static int max31790_init_client(struct i2c_client *client,
 				struct max31790_data *data)
 {
@@ -521,6 +567,10 @@ static int max31790_probe(struct i2c_client *client)
 	data->client = client;
 	mutex_init(&data->update_lock);
 
+	err = max31790_config_pwm_as_tach(dev, client);
+	if (err)
+		dev_crit(dev, "Config PWM as TACH failed.\n");
+
 	/*
 	 * Initialize the max31790 chip
 	 */
-- 
2.25.1