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    Subject[PATCH v5 2/2] 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: Andreas Klinger <ak@it-klinger.de>
    ---
    drivers/iio/adc/Kconfig | 19 ++
    drivers/iio/adc/Makefile | 1 +
    drivers/iio/adc/hx711.c | 531 +++++++++++++++++++++++++++++++++++++++++++++++
    3 files changed, 551 insertions(+)
    create mode 100644 drivers/iio/adc/hx711.c

    diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
    index 932de1f9d1e7..1dcf2ace1697 100644
    --- a/drivers/iio/adc/Kconfig
    +++ b/drivers/iio/adc/Kconfig
    @@ -205,6 +205,25 @@ 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
    diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
    index b1aa456e6af3..d46e289900ef 100644
    --- a/drivers/iio/adc/Makefile
    +++ b/drivers/iio/adc/Makefile
    @@ -21,6 +21,7 @@ obj-$(CONFIG_CC10001_ADC) += cc10001_adc.o
    obj-$(CONFIG_DA9150_GPADC) += da9150-gpadc.o
    obj-$(CONFIG_EXYNOS_ADC) += exynos_adc.o
    obj-$(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
    diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c
    new file mode 100644
    index 000000000000..e41414556158
    --- /dev/null
    +++ b/drivers/iio/adc/hx711.c
    @@ -0,0 +1,531 @@
    +/*
    + * 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 oszilloscope 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)) {
    + 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");
    +
    --
    2.1.4
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      Last update: 2017-01-05 19:02    [W:4.922 / U:0.012 seconds]
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