linux-kernel - [PATCH] iio: pressure: mpl115: Implementing low power mode by

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Date:   Tue, 27 Sep 2022 23:08:38 +0530
From:   Rajat Khandelwal <rajat.khandelwal@...el.com>
To:     jic23@...nel.org, lars@...afoo.de
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rajat Khandelwal <rajat.khandelwal@...el.com>
Subject: [PATCH] iio: pressure: mpl115: Implementing low power mode by

MPL115 supports shutdown gpio which can be used to set the default
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 sets the default mode to low-power and only exits when
a reading is required from the chip. This maximises 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 <rajat.khandelwal@...el.com>
---
 drivers/iio/pressure/mpl115.c | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/pressure/mpl115.c b/drivers/iio/pressure/mpl115.c
index 5bf5b9abe6f1..c0ad3e941d05 100644
--- a/drivers/iio/pressure/mpl115.c
+++ b/drivers/iio/pressure/mpl115.c
@@ -3,13 +3,12 @@
  * mpl115.c - Support for Freescale MPL115A pressure/temperature sensor
  *
  * Copyright (c) 2014 Peter Meerwald <pmeerw@...erw.net>
- *
- * TODO: shutdown pin
  */
 
 #include <linux/module.h>
 #include <linux/iio/iio.h>
 #include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 
 #include "mpl115.h"
 
@@ -27,6 +26,7 @@ struct mpl115_data {
 	s16 a0;
 	s16 b1, b2;
 	s16 c12;
+	struct gpio_desc *shutdown;
 	const struct mpl115_ops *ops;
 };
 
@@ -102,13 +102,27 @@ static int mpl115_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_PROCESSED:
-		ret = mpl115_comp_pressure(data, val, val2);
+		if (data->shutdown) {
+			gpiod_set_value(data->shutdown, 0);
+			usleep_range(5000, 6000);
+			ret = mpl115_comp_pressure(data, val, val2);
+			gpiod_set_value(data->shutdown, 1);
+		} else
+			ret = mpl115_comp_pressure(data, val, val2);
+
 		if (ret < 0)
 			return ret;
 		return IIO_VAL_INT_PLUS_MICRO;
 	case IIO_CHAN_INFO_RAW:
 		/* temperature -5.35 C / LSB, 472 LSB is 25 C */
-		ret = mpl115_read_temp(data);
+		if (data->shutdown) {
+			gpiod_set_value(data->shutdown, 0);
+			usleep_range(5000, 6000);
+			ret = mpl115_read_temp(data);
+			gpiod_set_value(data->shutdown, 1);
+		} else
+			ret = mpl115_read_temp(data);
+
 		if (ret < 0)
 			return ret;
 		*val = ret >> 6;
@@ -185,6 +199,17 @@ int mpl115_probe(struct device *dev, const char *name,
 		return ret;
 	data->c12 = ret;
 
+	data->shutdown = devm_gpiod_get_optional(dev, "shutdown",
+						 GPIOD_OUT_HIGH);
+	if (IS_ERR(data->shutdown))
+		return dev_err_probe(dev, PTR_ERR(data->shutdown),
+				     "cannot get shutdown gpio\n");
+
+	if (data->shutdown)
+		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);
-- 
2.34.1