Commit c3b2fdd0 authored by Andreas Klinger's avatar Andreas Klinger Committed by Jonathan Cameron
Browse files

iio: adc: hx711: Add IIO driver for AVIA HX711 



This is the IIO driver for AVIA HX711 ADC which is mostly used in weighting
cells.

The protocol is quite simple and using GPIOs:
One GPIO is used as clock (SCK) while another GPIO is read (DOUT)

The raw value read from the chip is delivered.
To get a weight one needs to subtract the zero offset and scale it.

Signed-off-by: default avatarAndreas Klinger <ak@it-klinger.de>
Signed-off-by: default avatarJonathan Cameron <jic23@kernel.org>
parent ff1293f6

drivers/iio/adc/Kconfig

+19 −0
Original line number Diff line number Diff line
@@ -247,6 +247,25 @@ config HI8435 
	  This driver can also be built as a module. If so, the module will be

	  called hi8435.



config HX711

	tristate "AVIA HX711 ADC for weight cells"

	depends on GPIOLIB

	help

	  If you say yes here you get support for AVIA HX711 ADC which is used

	  for weigh cells



	  This driver uses two GPIOs, one acts as the clock and controls the

	  channel selection and gain, the other one is used for the measurement

          data



	  Currently the raw value is read from the chip and delivered.

	  To get an actual weight one needs to subtract the

	  zero offset and multiply by a scale factor.

	  This should be done in userspace.



	  This driver can also be built as a module. If so, the module will be

	  called hx711.



config INA2XX_ADC

	tristate "Texas Instruments INA2xx Power Monitors IIO driver"

	depends on I2C && !SENSORS_INA2XX

drivers/iio/adc/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ obj-$(CONFIG_ENVELOPE_DETECTOR) += envelope-detector.o 
obj-$(CONFIG_EXYNOS_ADC) += exynos_adc.o

obj-$(CONFIG_FSL_MX25_ADC) += fsl-imx25-gcq.o

obj-$(CONFIG_HI8435) += hi8435.o

obj-$(CONFIG_HX711) += hx711.o

obj-$(CONFIG_IMX7D_ADC) += imx7d_adc.o

obj-$(CONFIG_INA2XX_ADC) += ina2xx-adc.o

obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o

drivers/iio/adc/hx711.c

0 → 100644
+532 −0
Original line number Diff line number Diff line 
/*

 * HX711: analog to digital converter for weight sensor module

 *

 * Copyright (c) 2016 Andreas Klinger <ak@it-klinger.de>

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

 * GNU General Public License for more details.

 */

#include <linux/err.h>

#include <linux/kernel.h>

#include <linux/module.h>

#include <linux/of.h>

#include <linux/platform_device.h>

#include <linux/property.h>

#include <linux/slab.h>

#include <linux/sched.h>

#include <linux/delay.h>

#include <linux/iio/iio.h>

#include <linux/iio/sysfs.h>

#include <linux/gpio/consumer.h>

#include <linux/regulator/consumer.h>



/* gain to pulse and scale conversion */

#define HX711_GAIN_MAX		3



struct hx711_gain_to_scale {

	int			gain;

	int			gain_pulse;

	int			scale;

	int			channel;

};



/*

 * .scale depends on AVDD which in turn is known as soon as the regulator

 * is available

 * therefore we set .scale in hx711_probe()

 *

 * channel A in documentation is channel 0 in source code

 * channel B in documentation is channel 1 in source code

 */

static struct hx711_gain_to_scale hx711_gain_to_scale[HX711_GAIN_MAX] = {

	{ 128, 1, 0, 0 },

	{  32, 2, 0, 1 },

	{  64, 3, 0, 0 }

};



static int hx711_get_gain_to_pulse(int gain)

{

	int i;



	for (i = 0; i < HX711_GAIN_MAX; i++)

		if (hx711_gain_to_scale[i].gain == gain)

			return hx711_gain_to_scale[i].gain_pulse;

	return 1;

}



static int hx711_get_gain_to_scale(int gain)

{

	int i;



	for (i = 0; i < HX711_GAIN_MAX; i++)

		if (hx711_gain_to_scale[i].gain == gain)

			return hx711_gain_to_scale[i].scale;

	return 0;

}



static int hx711_get_scale_to_gain(int scale)

{

	int i;



	for (i = 0; i < HX711_GAIN_MAX; i++)

		if (hx711_gain_to_scale[i].scale == scale)

			return hx711_gain_to_scale[i].gain;

	return -EINVAL;

}



struct hx711_data {

	struct device		*dev;

	struct gpio_desc	*gpiod_pd_sck;

	struct gpio_desc	*gpiod_dout;

	struct regulator	*reg_avdd;

	int			gain_set;	/* gain set on device */

	int			gain_chan_a;	/* gain for channel A */

	struct mutex		lock;

};



static int hx711_cycle(struct hx711_data *hx711_data)

{

	int val;



	/*

	 * if preempted for more then 60us while PD_SCK is high:

	 * hx711 is going in reset

	 * ==> measuring is false

	 */

	preempt_disable();

	gpiod_set_value(hx711_data->gpiod_pd_sck, 1);

	val = gpiod_get_value(hx711_data->gpiod_dout);

	/*

	 * here we are not waiting for 0.2 us as suggested by the datasheet,

	 * because the oscilloscope showed in a test scenario

	 * at least 1.15 us for PD_SCK high (T3 in datasheet)

	 * and 0.56 us for PD_SCK low on TI Sitara with 800 MHz

	 */

	gpiod_set_value(hx711_data->gpiod_pd_sck, 0);

	preempt_enable();



	return val;

}



static int hx711_read(struct hx711_data *hx711_data)

{

	int i, ret;

	int value = 0;

	int val = gpiod_get_value(hx711_data->gpiod_dout);



	/* we double check if it's really down */

	if (val)

		return -EIO;



	for (i = 0; i < 24; i++) {

		value <<= 1;

		ret = hx711_cycle(hx711_data);

		if (ret)

			value++;

	}



	value ^= 0x800000;



	for (i = 0; i < hx711_get_gain_to_pulse(hx711_data->gain_set); i++)

		hx711_cycle(hx711_data);



	return value;

}



static int hx711_wait_for_ready(struct hx711_data *hx711_data)

{

	int i, val;



	/*

	 * a maximum reset cycle time of 56 ms was measured.

	 * we round it up to 100 ms

	 */

	for (i = 0; i < 100; i++) {

		val = gpiod_get_value(hx711_data->gpiod_dout);

		if (!val)

			break;

		/* sleep at least 1 ms */

		msleep(1);

	}

	if (val)

		return -EIO;



	return 0;

}



static int hx711_reset(struct hx711_data *hx711_data)

{

	int ret;

	int val = gpiod_get_value(hx711_data->gpiod_dout);



	if (val) {

		/*

		 * an examination with the oszilloscope indicated

		 * that the first value read after the reset is not stable

		 * if we reset too short;

		 * the shorter the reset cycle

		 * the less reliable the first value after reset is;

		 * there were no problems encountered with a value

		 * of 10 ms or higher

		 */

		gpiod_set_value(hx711_data->gpiod_pd_sck, 1);

		msleep(10);

		gpiod_set_value(hx711_data->gpiod_pd_sck, 0);



		ret = hx711_wait_for_ready(hx711_data);

		if (ret)

			return ret;

		/*

		 * after a reset the gain is 128 so we do a dummy read

		 * to set the gain for the next read

		 */

		ret = hx711_read(hx711_data);

		if (ret < 0)

			return ret;



		/*

		 * after a dummy read we need to wait vor readiness

		 * for not mixing gain pulses with the clock

		 */

		ret = hx711_wait_for_ready(hx711_data);

		if (ret)

			return ret;

	}



	return val;

}



static int hx711_set_gain_for_channel(struct hx711_data *hx711_data, int chan)

{

	int ret;



	if (chan == 0) {

		if (hx711_data->gain_set == 32) {

			hx711_data->gain_set = hx711_data->gain_chan_a;



			ret = hx711_read(hx711_data);

			if (ret < 0)

				return ret;



			ret = hx711_wait_for_ready(hx711_data);

			if (ret)

				return ret;

		}

	} else {

		if (hx711_data->gain_set != 32) {

			hx711_data->gain_set = 32;



			ret = hx711_read(hx711_data);

			if (ret < 0)

				return ret;



			ret = hx711_wait_for_ready(hx711_data);

			if (ret)

				return ret;

		}

	}



	return 0;

}



static int hx711_read_raw(struct iio_dev *indio_dev,

				const struct iio_chan_spec *chan,

				int *val, int *val2, long mask)

{

	struct hx711_data *hx711_data = iio_priv(indio_dev);

	int ret;



	switch (mask) {

	case IIO_CHAN_INFO_RAW:

		mutex_lock(&hx711_data->lock);



		/*

		 * hx711_reset() must be called from here

		 * because it could be calling hx711_read() by itself

		 */

		if (hx711_reset(hx711_data)) {

			mutex_unlock(&hx711_data->lock);

			dev_err(hx711_data->dev, "reset failed!");

			return -EIO;

		}



		ret = hx711_set_gain_for_channel(hx711_data, chan->channel);

		if (ret < 0) {

			mutex_unlock(&hx711_data->lock);

			return ret;

		}



		*val = hx711_read(hx711_data);



		mutex_unlock(&hx711_data->lock);



		if (*val < 0)

			return *val;

		return IIO_VAL_INT;

	case IIO_CHAN_INFO_SCALE:

		*val = 0;

		mutex_lock(&hx711_data->lock);



		*val2 = hx711_get_gain_to_scale(hx711_data->gain_set);



		mutex_unlock(&hx711_data->lock);



		return IIO_VAL_INT_PLUS_NANO;

	default:

		return -EINVAL;

	}

}



static int hx711_write_raw(struct iio_dev *indio_dev,

				struct iio_chan_spec const *chan,

				int val,

				int val2,

				long mask)

{

	struct hx711_data *hx711_data = iio_priv(indio_dev);

	int ret;

	int gain;



	switch (mask) {

	case IIO_CHAN_INFO_SCALE:

		/*

		 * a scale greater than 1 mV per LSB is not possible

		 * with the HX711, therefore val must be 0

		 */

		if (val != 0)

			return -EINVAL;



		mutex_lock(&hx711_data->lock);



		gain = hx711_get_scale_to_gain(val2);

		if (gain < 0) {

			mutex_unlock(&hx711_data->lock);

			return gain;

		}



		if (gain != hx711_data->gain_set) {

			hx711_data->gain_set = gain;

			if (gain != 32)

				hx711_data->gain_chan_a = gain;



			ret = hx711_read(hx711_data);

			if (ret < 0) {

				mutex_unlock(&hx711_data->lock);

				return ret;

			}

		}



		mutex_unlock(&hx711_data->lock);

		return 0;

	default:

		return -EINVAL;

	}



	return 0;

}



static int hx711_write_raw_get_fmt(struct iio_dev *indio_dev,

		struct iio_chan_spec const *chan,

		long mask)

{

	return IIO_VAL_INT_PLUS_NANO;

}



static ssize_t hx711_scale_available_show(struct device *dev,

				struct device_attribute *attr,

				char *buf)

{

	struct iio_dev_attr *iio_attr = to_iio_dev_attr(attr);

	int channel = iio_attr->address;

	int i, len = 0;



	for (i = 0; i < HX711_GAIN_MAX; i++)

		if (hx711_gain_to_scale[i].channel == channel)

			len += sprintf(buf + len, "0.%09d ",

					hx711_gain_to_scale[i].scale);



	len += sprintf(buf + len, "\n");



	return len;

}



static IIO_DEVICE_ATTR(in_voltage0_scale_available, S_IRUGO,

	hx711_scale_available_show, NULL, 0);



static IIO_DEVICE_ATTR(in_voltage1_scale_available, S_IRUGO,

	hx711_scale_available_show, NULL, 1);



static struct attribute *hx711_attributes[] = {

	&iio_dev_attr_in_voltage0_scale_available.dev_attr.attr,

	&iio_dev_attr_in_voltage1_scale_available.dev_attr.attr,

	NULL,

};



static struct attribute_group hx711_attribute_group = {

	.attrs = hx711_attributes,

};



static const struct iio_info hx711_iio_info = {

	.driver_module		= THIS_MODULE,

	.read_raw		= hx711_read_raw,

	.write_raw		= hx711_write_raw,

	.write_raw_get_fmt	= hx711_write_raw_get_fmt,

	.attrs			= &hx711_attribute_group,

};



static const struct iio_chan_spec hx711_chan_spec[] = {

	{

		.type = IIO_VOLTAGE,

		.channel = 0,

		.indexed = 1,

		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),

		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),

	},

	{

		.type = IIO_VOLTAGE,

		.channel = 1,

		.indexed = 1,

		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),

		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),

	},

};



static int hx711_probe(struct platform_device *pdev)

{

	struct device *dev = &pdev->dev;

	struct hx711_data *hx711_data;

	struct iio_dev *indio_dev;

	int ret;

	int i;



	indio_dev = devm_iio_device_alloc(dev, sizeof(struct hx711_data));

	if (!indio_dev) {

		dev_err(dev, "failed to allocate IIO device\n");

		return -ENOMEM;

	}



	hx711_data = iio_priv(indio_dev);

	hx711_data->dev = dev;



	mutex_init(&hx711_data->lock);



	/*

	 * PD_SCK stands for power down and serial clock input of HX711

	 * in the driver it is an output

	 */

	hx711_data->gpiod_pd_sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);

	if (IS_ERR(hx711_data->gpiod_pd_sck)) {

		dev_err(dev, "failed to get sck-gpiod: err=%ld\n",

					PTR_ERR(hx711_data->gpiod_pd_sck));

		return PTR_ERR(hx711_data->gpiod_pd_sck);

	}



	/*

	 * DOUT stands for serial data output of HX711

	 * for the driver it is an input

	 */

	hx711_data->gpiod_dout = devm_gpiod_get(dev, "dout", GPIOD_IN);

	if (IS_ERR(hx711_data->gpiod_dout)) {

		dev_err(dev, "failed to get dout-gpiod: err=%ld\n",

					PTR_ERR(hx711_data->gpiod_dout));

		return PTR_ERR(hx711_data->gpiod_dout);

	}



	hx711_data->reg_avdd = devm_regulator_get(dev, "avdd");

	if (IS_ERR(hx711_data->reg_avdd))

		return PTR_ERR(hx711_data->reg_avdd);



	ret = regulator_enable(hx711_data->reg_avdd);

	if (ret < 0)

		return ret;



	/*

	 * with

	 * full scale differential input range: AVDD / GAIN

	 * full scale output data: 2^24

	 * we can say:

	 *     AVDD / GAIN = 2^24

	 * therefore:

	 *     1 LSB = AVDD / GAIN / 2^24

	 * AVDD is in uV, but we need 10^-9 mV

	 * approximately to fit into a 32 bit number:

	 * 1 LSB = (AVDD * 100) / GAIN / 1678 [10^-9 mV]

	 */

	ret = regulator_get_voltage(hx711_data->reg_avdd);

	if (ret < 0) {

		regulator_disable(hx711_data->reg_avdd);

		return ret;

	}

	/* we need 10^-9 mV */

	ret *= 100;



	for (i = 0; i < HX711_GAIN_MAX; i++)

		hx711_gain_to_scale[i].scale =

			ret / hx711_gain_to_scale[i].gain / 1678;



	hx711_data->gain_set = 128;

	hx711_data->gain_chan_a = 128;



	platform_set_drvdata(pdev, indio_dev);



	indio_dev->name = "hx711";

	indio_dev->dev.parent = &pdev->dev;

	indio_dev->info = &hx711_iio_info;

	indio_dev->modes = INDIO_DIRECT_MODE;

	indio_dev->channels = hx711_chan_spec;

	indio_dev->num_channels = ARRAY_SIZE(hx711_chan_spec);



	ret = iio_device_register(indio_dev);

	if (ret < 0) {

		dev_err(dev, "Couldn't register the device\n");

		regulator_disable(hx711_data->reg_avdd);

	}



	return ret;

}



static int hx711_remove(struct platform_device *pdev)

{

	struct hx711_data *hx711_data;

	struct iio_dev *indio_dev;



	indio_dev = platform_get_drvdata(pdev);

	hx711_data = iio_priv(indio_dev);



	iio_device_unregister(indio_dev);



	regulator_disable(hx711_data->reg_avdd);



	return 0;

}



static const struct of_device_id of_hx711_match[] = {

	{ .compatible = "avia,hx711", },

	{},

};



MODULE_DEVICE_TABLE(of, of_hx711_match);



static struct platform_driver hx711_driver = {

	.probe		= hx711_probe,

	.remove		= hx711_remove,

	.driver		= {

		.name		= "hx711-gpio",

		.of_match_table	= of_hx711_match,

	},

};



module_platform_driver(hx711_driver);



MODULE_AUTHOR("Andreas Klinger <ak@it-klinger.de>");

MODULE_DESCRIPTION("HX711 bitbanging driver - ADC for weight cells");

MODULE_LICENSE("GPL");

MODULE_ALIAS("platform:hx711-gpio");

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