iio: humidity: hdc3020: add reset management

The HDC3020 provides an active low reset signal that must be handled if
connected. Asserting this signal turns the device into Trigger-on Demand
measurement mode, reducing its power consumption when no measurements
are required like in low-power modes.

According to the datasheet, the longest "Reset Ready" is 3 ms, which is
only taken into account if the reset signal is defined.

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://lore.kernel.org/r/20240303-hdc3020-pm-v3-3-48bc02b5241b@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/humidity/hdc3020.c

@@ -15,6 +15,7 @@
 #include <linux/cleanup.h>
 #include <linux/crc8.h>
 #include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 #include <linux/i2c.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
@@ -70,6 +71,7 @@
 
 struct hdc3020_data {
 	struct i2c_client *client;
+	struct gpio_desc *reset_gpio;
 	struct regulator *vdd_supply;
 	/*
 	 * Ensure that the sensor configuration (currently only heater is
@@ -558,6 +560,9 @@ static int hdc3020_power_off(struct hdc3020_data *data)
 {
 	hdc3020_exec_cmd(data, HDC3020_EXIT_AUTO);
 
+	if (data->reset_gpio)
+		gpiod_set_value_cansleep(data->reset_gpio, 1);
+
 	return regulator_disable(data->vdd_supply);
 }
 
@@ -571,6 +576,11 @@ static int hdc3020_power_on(struct hdc3020_data *data)
 
 	fsleep(5000);
 
+	if (data->reset_gpio) {
+		gpiod_set_value_cansleep(data->reset_gpio, 0);
+		fsleep(3000);
+	}
+
 	if (data->client->irq) {
 		/*
 		 * The alert output is activated by default upon power up,
@@ -627,6 +637,12 @@ static int hdc3020_probe(struct i2c_client *client)
 		return dev_err_probe(&client->dev, PTR_ERR(data->vdd_supply),
 				     "Unable to get VDD regulator\n");
 
+	data->reset_gpio = devm_gpiod_get_optional(&client->dev, "reset",
+						   GPIOD_OUT_HIGH);
+	if (IS_ERR(data->reset_gpio))
+		return dev_err_probe(&client->dev, PTR_ERR(data->reset_gpio),
+				     "Cannot get reset GPIO\n");
+
 	ret = hdc3020_power_on(data);
 	if (ret)
 		return dev_err_probe(&client->dev, ret, "Power on failed\n");