iio: pressure: mpl115: Implementing low power mode by shutdown gpio

MPL115 supports shutdown gpio which can be used to set the state
to low power mode. Power from all internal circuits and
registers is removed. This is done by pulling the SHDN pin to low.
This patch enables runtime PM on MPL115 to increase power savings.

According to spec., a wakeup time period of ~5 ms exists between
waking up and actually communicating with the device. This is
implemented using sleep delay.

Signed-off-by: Rajat Khandelwal <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/pressure/mpl115.c

···
  *
  * Copyright (c) 2014 Peter Meerwald <[e-mail]>
  *
- * TODO: shutdown pin
+ * TODO: synchronization with system suspend
  */
 
 #include <linux/module.h>
 #include <linux/iio/iio.h>
 #include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 
 #include "mpl115.h"
 
···
 	s16 a0;
 	s16 b1, b2;
 	s16 c12;
+	struct gpio_desc *shutdown;
 	const struct mpl115_ops *ops;
 };
 
···
 
 	switch (mask) {
 	case IIO_CHAN_INFO_PROCESSED:
+		pm_runtime_get_sync(data->dev);
 		ret = mpl115_comp_pressure(data, val, val2);
 		if (ret < 0)
 			return ret;
+		pm_runtime_mark_last_busy(data->dev);
+		pm_runtime_put_autosuspend(data->dev);
+
 		return IIO_VAL_INT_PLUS_MICRO;
 	case IIO_CHAN_INFO_RAW:
+		pm_runtime_get_sync(data->dev);
 		/* temperature -5.35 C / LSB, 472 LSB is 25 C */
 		ret = mpl115_read_temp(data);
 		if (ret < 0)
 			return ret;
+		pm_runtime_mark_last_busy(data->dev);
+		pm_runtime_put_autosuspend(data->dev);
 		*val = ret >> 6;
+
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_OFFSET:
 		*val = -605;
···
 	if (ret)
 		return ret;
 
+	dev_set_drvdata(dev, indio_dev);
+
 	ret = data->ops->read(data->dev, MPL115_A0);
 	if (ret < 0)
 		return ret;
···
 		return ret;
 	data->c12 = ret;
 
+	data->shutdown = devm_gpiod_get_optional(dev, "shutdown",
+						 GPIOD_OUT_LOW);
+	if (IS_ERR(data->shutdown))
+		return dev_err_probe(dev, PTR_ERR(data->shutdown),
+				     "cannot get shutdown gpio\n");
+
+	if (data->shutdown) {
+		/* Enable runtime PM */
+		pm_runtime_get_noresume(dev);
+		pm_runtime_set_active(dev);
+		pm_runtime_enable(dev);
+
+		/*
+		 * As the device takes 3 ms to come up with a fresh
+		 * reading after power-on and 5 ms to actually power-on,
+		 * do not shut it down unnecessarily. Set autosuspend to
+		 * 2000 ms.
+		 */
+		pm_runtime_set_autosuspend_delay(dev, 2000);
+		pm_runtime_use_autosuspend(dev);
+		pm_runtime_put(dev);
+
+		dev_dbg(dev, "low-power mode enabled");
+	} else
+		dev_dbg(dev, "low-power mode disabled");
+
 	return devm_iio_device_register(dev, indio_dev);
 }
 EXPORT_SYMBOL_NS_GPL(mpl115_probe, IIO_MPL115);
+
+static int mpl115_runtime_suspend(struct device *dev)
+{
+	struct mpl115_data *data = iio_priv(dev_get_drvdata(dev));
+
+	gpiod_set_value(data->shutdown, 1);
+
+	return 0;
+}
+
+static int mpl115_runtime_resume(struct device *dev)
+{
+	struct mpl115_data *data = iio_priv(dev_get_drvdata(dev));
+
+	gpiod_set_value(data->shutdown, 0);
+	usleep_range(5000, 6000);
+
+	return 0;
+}
+
+EXPORT_NS_RUNTIME_DEV_PM_OPS(mpl115_dev_pm_ops, mpl115_runtime_suspend,
+			  mpl115_runtime_resume, NULL, IIO_MPL115);
 
 MODULE_AUTHOR("Peter Meerwald <[e-mail]>");
 MODULE_DESCRIPTION("Freescale MPL115 pressure/temperature driver");

drivers/iio/pressure/mpl115.h

···
  * Copyright (c) 2016 Akinobu Mita <[e-mail]>
  */
 
+#include <linux/pm_runtime.h>
+
 #ifndef _MPL115_H_
 #define _MPL115_H_
 
···
 
 int mpl115_probe(struct device *dev, const char *name,
 			const struct mpl115_ops *ops);
+
+/*PM ops */
+extern const struct dev_pm_ops mpl115_dev_pm_ops;
 
 #endif

drivers/iio/pressure/mpl115_i2c.c

···
 static struct i2c_driver mpl115_i2c_driver = {
 	.driver = {
 		.name	= "mpl115",
+		.pm = pm_ptr(&mpl115_dev_pm_ops),
 	},
 	.probe = mpl115_i2c_probe,
 	.id_table = mpl115_i2c_id,

drivers/iio/pressure/mpl115_spi.c

···
 static struct spi_driver mpl115_spi_driver = {
 	.driver = {
 		.name   = "mpl115",
+		.pm = pm_ptr(&mpl115_dev_pm_ops),
 	},
 	.probe = mpl115_spi_probe,
 	.id_table = mpl115_spi_ids,