Date:   Sun, 8 Jan 2017 16:43:49 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Andreas Klinger <ak@...klinger.de>, devicetree@...r.kernel.org,
        linux-iio@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, robh+dt@...nel.org,
        pawel.moll@....com, mark.rutland@....com,
        ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
        knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net
Subject: Re: [PATCH v5 2/2] iio: adc: hx711: Add IIO driver for AVIA HX711

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@...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.
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@...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@...klinger.de>");
>> +MODULE_DESCRIPTION("HX711 bitbanging driver - ADC for weight cells");
>> +MODULE_LICENSE("GPL");
>> +MODULE_ALIAS("platform:hx711-gpio");
>> +
>>
> 
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