iio: srf04: add power management feature

Add suspend and resume operations for being used by optional power
management.

The suspend function is switching off an GPIO which can be used by the
hardware to switch power off. The resume function is switching the GPIO
on and sleeps an adjustable time to give the device a chance to be up
and running.

If activated the driver gets into autosuspend after some time of
inactivity.
Suggested-by: Franz Parzer <rpi-receiver@htl-steyr.ac.at>
Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/proximity/srf04.c

@@ -45,6 +45,7 @@
 #include <linux/sched.h>
 #include <linux/interrupt.h>
 #include <linux/delay.h>
+#include <linux/pm_runtime.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
 
@@ -56,6 +57,7 @@ struct srf04_data {
 	struct device		*dev;
 	struct gpio_desc	*gpiod_trig;
 	struct gpio_desc	*gpiod_echo;
+	struct gpio_desc	*gpiod_power;
 	struct mutex		lock;
 	int			irqnr;
 	ktime_t			ts_rising;
@@ -63,6 +65,7 @@ struct srf04_data {
 	struct completion	rising;
 	struct completion	falling;
 	const struct srf04_cfg	*cfg;
+	int			startup_time_ms;
 };
 
 static const struct srf04_cfg srf04_cfg = {
@@ -97,6 +100,9 @@ static int srf04_read(struct srf04_data *data)
 	u64 dt_ns;
 	u32 time_ns, distance_mm;
 
+	if (data->gpiod_power)
+		pm_runtime_get_sync(data->dev);
+
 	/*
 	 * just one read-echo-cycle can take place at a time
 	 * ==> lock against concurrent reading calls
@@ -110,6 +116,11 @@ static int srf04_read(struct srf04_data *data)
 	udelay(data->cfg->trigger_pulse_us);
 	gpiod_set_value(data->gpiod_trig, 0);
 
+	if (data->gpiod_power) {
+		pm_runtime_mark_last_busy(data->dev);
+		pm_runtime_put_autosuspend(data->dev);
+	}
+
 	/* it should not take more than 20 ms until echo is rising */
 	ret = wait_for_completion_killable_timeout(&data->rising, HZ/50);
 	if (ret < 0) {
@@ -268,6 +279,22 @@ static int srf04_probe(struct platform_device *pdev)
 		return PTR_ERR(data->gpiod_echo);
 	}
 
+	data->gpiod_power = devm_gpiod_get_optional(dev, "power",
+								GPIOD_OUT_LOW);
+	if (IS_ERR(data->gpiod_power)) {
+		dev_err(dev, "failed to get power-gpios: err=%ld\n",
+						PTR_ERR(data->gpiod_power));
+		return PTR_ERR(data->gpiod_power);
+	}
+	if (data->gpiod_power) {
+
+		if (of_property_read_u32(dev->of_node, "startup-time-ms",
+						&data->startup_time_ms))
+			data->startup_time_ms = 100;
+		dev_dbg(dev, "using power gpio: startup-time-ms=%d\n",
+							data->startup_time_ms);
+	}
+
 	if (gpiod_cansleep(data->gpiod_echo)) {
 		dev_err(data->dev, "cansleep-GPIOs not supported\n");
 		return -ENODEV;
@@ -296,14 +323,81 @@ static int srf04_probe(struct platform_device *pdev)
 	indio_dev->channels = srf04_chan_spec;
 	indio_dev->num_channels = ARRAY_SIZE(srf04_chan_spec);
 
-	return devm_iio_device_register(dev, indio_dev);
+	ret = iio_device_register(indio_dev);
+	if (ret < 0) {
+		dev_err(data->dev, "iio_device_register: %d\n", ret);
+		return ret;
+	}
+
+	if (data->gpiod_power) {
+		pm_runtime_set_autosuspend_delay(data->dev, 1000);
+		pm_runtime_use_autosuspend(data->dev);
+
+		ret = pm_runtime_set_active(data->dev);
+		if (ret) {
+			dev_err(data->dev, "pm_runtime_set_active: %d\n", ret);
+			iio_device_unregister(indio_dev);
+		}
+
+		pm_runtime_enable(data->dev);
+		pm_runtime_idle(data->dev);
+	}
+
+	return ret;
 }
 
+static int srf04_remove(struct platform_device *pdev)
+{
+	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
+	struct srf04_data *data = iio_priv(indio_dev);
+
+	iio_device_unregister(indio_dev);
+
+	if (data->gpiod_power) {
+		pm_runtime_disable(data->dev);
+		pm_runtime_set_suspended(data->dev);
+	}
+
+	return 0;
+}
+
+static int __maybe_unused srf04_pm_runtime_suspend(struct device *dev)
+{
+	struct platform_device *pdev = container_of(dev,
+						struct platform_device, dev);
+	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
+	struct srf04_data *data = iio_priv(indio_dev);
+
+	gpiod_set_value(data->gpiod_power, 0);
+
+	return 0;
+}
+
+static int __maybe_unused srf04_pm_runtime_resume(struct device *dev)
+{
+	struct platform_device *pdev = container_of(dev,
+						struct platform_device, dev);
+	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
+	struct srf04_data *data = iio_priv(indio_dev);
+
+	gpiod_set_value(data->gpiod_power, 1);
+	msleep(data->startup_time_ms);
+
+	return 0;
+}
+
+static const struct dev_pm_ops srf04_pm_ops = {
+	SET_RUNTIME_PM_OPS(srf04_pm_runtime_suspend,
+				srf04_pm_runtime_resume, NULL)
+};
+
 static struct platform_driver srf04_driver = {
 	.probe		= srf04_probe,
+	.remove		= srf04_remove,
 	.driver		= {
 		.name		= "srf04-gpio",
 		.of_match_table	= of_srf04_match,
+		.pm		= &srf04_pm_ops,
 	},
 };