Date:   Wed, 21 Dec 2016 19:16:45 +0100 (CET)
From:   Peter Meerwald-Stadler <pmeerw@...erw.net>
To:     Andreas Klinger <ak@...klinger.de>
cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        jic23@...nel.org, knaack.h@....de, lars@...afoo.de
Subject: Re: [PATCH v4 2/2] iio: adc: hx711: Add IIO driver for AVIA HX711


> 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 <ak@...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 <ak@...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 <ak@...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)

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