[PATCH v2] iio: pressure: mpl115: Implementing low power mode by shutdown gpio

[PATCH v2] iio: pressure: mpl115: Implementing low power mode by shutdown gpio

[Rajat Khandelwal]

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@intel.com>
---

v2: Grammatically completing subject line

 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@pmeerw.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

Re: [PATCH v2] iio: pressure: mpl115: Implementing low power mode by shutdown gpio

[Jonathan Cameron]

On Tue, 27 Sep 2022 23:12:12 +0530
Rajat Khandelwal <rajat.khandelwal@intel.com> wrote:

> 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@intel.com>
Ah. I missed there was a v2 and replied to v1.

> ---
> 
> v2: Grammatically completing subject line
> 
>  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@pmeerw.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);

RE: [PATCH v2] iio: pressure: mpl115: Implementing low power mode by shutdown gpio

[Khandelwal, Rajat]

>>Ah. I missed there was a v2 and replied to v1.
No problem Jon and thanks for the suggestion. A delay of 5ms
was not worth it when calculation itself takes only ~3ms. 
I have implemented runtime PM keeping a delay of 200 ms
which I think should suffice. Have sent you v3. 

-----Original Message-----
From: Jonathan Cameron <jic23@kernel.org> 
Sent: Sunday, October 2, 2022 6:52 PM
To: Khandelwal, Rajat <rajat.khandelwal@intel.com>
Cc: lars@metafoo.de; linux-iio@vger.kernel.org; linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] iio: pressure: mpl115: Implementing low power mode by shutdown gpio

On Tue, 27 Sep 2022 23:12:12 +0530
Rajat Khandelwal <rajat.khandelwal@intel.com> wrote:

> 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@intel.com>
Ah. I missed there was a v2 and replied to v1.

> ---
> 
> v2: Grammatically completing subject line
> 
>  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@pmeerw.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);