> This is the IIO driver for AVIA HX711 ADC which ist mostly used in weighting
> cells.
comments below
> 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 <a...@it-klinger.de>
> ---
> drivers/iio/adc/Kconfig | 19 ++
> drivers/iio/adc/Makefile | 1 +
> drivers/iio/adc/hx711.c | 466
> +++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 486 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..f4b5f587e9c0
> --- /dev/null
> +++ b/drivers/iio/adc/hx711.c
> @@ -0,0 +1,466 @@
> +/*
> + * HX711: analog to digital converter for weight sensor module
> + *
> + * Copyright (c) 2016 Andreas Klinger <a...@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_CHAN_A 0 /* channel id for A */
> +#define HX711_CHAN_B 1 /* channel id for B */
> +
> +#define HX711_GAIN_MAX 3
> +
> +struct hx711_gain_to_scale {
> + int gain;
> + int gain_pulse;
> + int scale;
> + int channel;
> +};
> +
> +static struct hx711_gain_to_scale hx711_gain_to_scale[HX711_GAIN_MAX] = {
> + { 128, 1, 0, HX711_CHAN_A },
> + { 32, 2, 0, HX711_CHAN_B },
> + { 64, 3, 0, HX711_CHAN_A }
> +};
> +
> +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;
.scale is set in _probe(), this was not obvious at first; maybe a comment?
> + 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_read(struct hx711_data *hx711_data);
> +
> +static int hx711_reset(struct hx711_data *hx711_data)
> +{
> + int ret;
> + int val = gpiod_get_value(hx711_data->gpiod_dout);
> +
> + if (val) {
> + int i;
> +
> + /*
> + * 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);
> +
> + /*
> + * 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);
> + }
> +
> + /*
> + * 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;
> + }
> +
> + return val;
> +}
> +
> +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;
> +
> + if (hx711_reset(hx711_data)) {
> + dev_err(hx711_data->dev, "reset failed!");
> + 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_set_gain_for_channel(struct hx711_data *hx711_data, int
> chan)
> +{
> + int ret;
> +
> + if (chan == HX711_CHAN_A) {
> + 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;
> + }
> + } else {
> + if (hx711_data->gain_set != 32) {
> + hx711_data->gain_set = 32;
> +
> + ret = hx711_read(hx711_data);
> + if (ret < 0)
> + return ret;
> + }
> + }
> +
> + return 0;
> +}
> +
> +static int hx711_read_raw(struct iio_dev *iio_dev,
> + const struct iio_chan_spec *chan,
> + int *val, int *val2, long mask)
> +{
> + struct hx711_data *hx711_data = iio_priv(iio_dev);
> + int ret;
> +
> + mutex_lock(&hx711_data->lock);
I suggest to move the locking into the case blocks where it is needed...
> +
> + switch (mask) {
> + case IIO_CHAN_INFO_RAW:
> + 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;
> + *val2 = hx711_get_gain_to_scale(hx711_data->gain_set);
> + mutex_unlock(&hx711_data->lock);
> + return IIO_VAL_INT_PLUS_NANO;
> + default:
> + mutex_unlock(&hx711_data->lock);
... this is quite ugly
> + return -EINVAL;
> + }
> +}
> +
> +static int hx711_write_raw(struct iio_dev *iio_dev,
> + struct iio_chan_spec const *chan,
> + int val,
> + int val2,
> + long mask)
> +{
> + struct hx711_data *hx711_data = iio_priv(iio_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)
> +{
> + return sprintf(buf, "0.%09d 0.%09d 0.%09d\n",
> + hx711_gain_to_scale[0].scale,
> + hx711_gain_to_scale[2].scale,
> + hx711_gain_to_scale[1].scale);
> +}
> +
> +static IIO_DEVICE_ATTR(scale_available, S_IRUGO,
> + hx711_scale_available_show, NULL, 0);
> +
> +static struct attribute *hx711_attributes[] = {
> + &iio_dev_attr_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 = HX711_CHAN_A,
> + .indexed = 1,
> + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
> + },
> + {
> + .type = IIO_VOLTAGE,
> + .channel = HX711_CHAN_B,
> + .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 *iio;
> + int ret;
> + int i;
> +
> + iio = devm_iio_device_alloc(dev, sizeof(struct hx711_data));
> + if (!iio) {
> + dev_err(dev, "failed to allocate IIO device\n");
> + return -ENOMEM;
> + }
> +
> + hx711_data = iio_priv(iio);
> + 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)
disable regulator
> + 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, iio);
> +
> + iio->name = "hx711";
> + iio->dev.parent = &pdev->dev;
> + iio->info = &hx711_iio_info;
> + iio->modes = INDIO_DIRECT_MODE;
> + iio->channels = hx711_chan_spec;
> + iio->num_channels = ARRAY_SIZE(hx711_chan_spec);
> +
> + return devm_iio_device_register(dev, iio);
disable regulator if this fails
> +}
> +
> +static int hx711_remove(struct platform_device *pdev)
> +{
> + struct hx711_data *hx711_data;
> + struct iio_dev *iio;
> +
> + iio = platform_get_drvdata(pdev);
> + hx711_data = iio_priv(iio);
> +
devm_iio_device_register and _remove() doesn't mix
> + 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 <a...@it-klinger.de>");
> +MODULE_DESCRIPTION("HX711 bitbanging driver - ADC for weight cells");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:hx711-gpio");
> +
>
--
Peter Meerwald-Stadler
+43-664-2444418 (mobile)
