[PATCH v5 2/2] iio: adc: hx711: Add IIO driver for AVIA HX711

[PATCH v5 2/2] iio: adc: hx711: Add IIO driver for AVIA HX711

[Andreas Klinger]

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

Re: [PATCH v5 2/2] iio: adc: hx711: Add IIO driver for AVIA HX711

[Jonathan Cameron]

On 05/01/17 17:51, Andreas Klinger wrote:
> 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>
I think your locking is a little heavy handed, perhaps a follow up patch to
relax it a little.

I fixed a trivial typo when applying.

Applied to the togreg branch of iio.git and pushed out as testing for the
autobuilders to play with it.

Thanks,

Jonathan
> ---
>  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
oscilloscope
> +		 * 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)) {
No unlock in this error path.
> +			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);
> +
Looking feels overly paranoid here as we are only accessing locally stored
data.  Still it's not actively doing any harm...
> +		*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");
> +
> 

Re: [PATCH v5 2/2] iio: adc: hx711: Add IIO driver for AVIA HX711

[Jonathan Cameron]

On 08/01/17 11:12, Jonathan Cameron wrote:
> On 05/01/17 17:51, Andreas Klinger wrote:
>> 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-n176/SwNRljddJNmlsFzeA@public.gmane.org>
> I think your locking is a little heavy handed, perhaps a follow up patch to
> relax it a little.
> 
> I fixed a trivial typo when applying.
> 
> Applied to the togreg branch of iio.git and pushed out as testing for the
> autobuilders to play with it.
And I forgot to fix the missing mutex_unlock.  Good thing zeroday caught that.

Updated and pushed out again for another round of build tests.

Jonathan
> 
> Thanks,
> 
> Jonathan
>> ---
>>  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-n176/SwNRljddJNmlsFzeA@public.gmane.org>
>> + *
>> + * 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
> oscilloscope
>> +		 * 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)) {
> No unlock in this error path.
>> +			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);
>> +
> Looking feels overly paranoid here as we are only accessing locally stored
> data.  Still it's not actively doing any harm...
>> +		*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-n176/SwNRljddJNmlsFzeA@public.gmane.org>");
>> +MODULE_DESCRIPTION("HX711 bitbanging driver - ADC for weight cells");
>> +MODULE_LICENSE("GPL");
>> +MODULE_ALIAS("platform:hx711-gpio");
>> +
>>
> 
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