Date:   Mon, 19 Dec 2016 20:49:58 +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 v3 2/2] iio: adc: hx711: Add IIO driver for AVIA HX711

On 14/12/16 16:17, Andreas Klinger wrote:
> This is the IIO driver for AVIA HX711 ADC which ist 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)
Youch. Controlling the next conversion via the number of clocks is hideous!
Oh well, guess it's one solution that limits the number of wires needed.

Still not as hideous as some ;) (sht15 I'm looking at you :)

Few comments inline.

Jonathan

> 
> 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  |  18 +++
>  drivers/iio/adc/Makefile |   1 +
>  drivers/iio/adc/hx711.c  | 292 +++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 311 insertions(+)
>  create mode 100644 drivers/iio/adc/hx711.c
> 
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index 932de1f9d1e7..918f582288c9 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -205,6 +205,24 @@ 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 weight cells
Typically just called weigh cells rather than weight cells.
One of those ugly bits of English.
> +
> +	  This driver uses two GPIOs, one for setting the clock and the other
> +	  one for getting the data
This driver uses two GPIOs, one acts as the clock and controls the channel
selection and gain, the other is used for the measurement data
(or something like that).
> +
> +	  Currently the raw value is read from the chip and delivered.
> +	  For getting an actual weight one needs to subtract the
To get an actual weight...
> +	  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..700281932ff0
> --- /dev/null
> +++ b/drivers/iio/adc/hx711.c
> @@ -0,0 +1,292 @@
> +/*
> + * 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.
> + *
No need for this blank line.
> + */
> +#include <linux/err.h>
> +#include <linux/gpio.h>
> +#include <linux/gpio/consumer.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>
> +
> +#define HX711_GAIN_32		2	/* gain = 32 for channel B  */
> +#define HX711_GAIN_64		3	/* gain = 64 for channel A  */
> +#define HX711_GAIN_128		1	/* gain = 128 for channel A */
> +
> +struct hx711_data {
> +	struct device		*dev;
> +	struct gpio_desc	*gpiod_sck;
> +	struct gpio_desc	*gpiod_dout;
> +	int			gain_pulse;
> +	struct mutex		lock;
> +};
> +
> +static int hx711_reset(struct hx711_data *hx711_data)
> +{
> +	int i, val;
> +
> +	val = gpiod_get_value(hx711_data->gpiod_dout);
> +	if (val) {
> +		gpiod_set_value(hx711_data->gpiod_sck, 1);
> +		udelay(80);
a comment here on why 80 would be good (it's bigger than 60?)
> +		gpiod_set_value(hx711_data->gpiod_sck, 0);
> +
> +		for (i = 0; i < 1000; i++) {
> +			val = gpiod_get_value(hx711_data->gpiod_dout);
> +			if (!val)
> +				break;
> +			/* sleep at least 1 ms */
> +			msleep(1);
> +		}
> +	}
> +
> +	return val;
> +}
> +
> +static int hx711_cycle(struct hx711_data *hx711_data)
> +{
> +	int val;
> +
/*
 * if pre...
> +	/* if preempted for more then 60us while SCK is high:
> +	 * hx711 is going in reset
> +	 * ==> measuring is false
> +	 */
> +	preempt_disable();
> +	gpiod_set_value(hx711_data->gpiod_sck, 1);
I'm reading the datasheet as suggesting you need to wait at least 0.1 microsecs
here...
> +	val = gpiod_get_value(hx711_data->gpiod_dout);
> +	gpiod_set_value(hx711_data->gpiod_sck, 0);
> +	preempt_enable();
> +
> +	return val;
> +}
> +
> +static int hx711_read(struct hx711_data *hx711_data)
> +{
> +	int i, ret;
> +	int value = 0;
> +
> +	mutex_lock(&hx711_data->lock);
> +
> +	if (hx711_reset(hx711_data)) {
> +		dev_err(hx711_data->dev, "reset failed!");
> +		mutex_unlock(&hx711_data->lock);
> +		return -1;
> +	}
> +
> +	for (i = 0; i < 24; i++) {
> +		value <<= 1;
> +		ret = hx711_cycle(hx711_data);
> +		if (ret)
> +			value++;
> +	}
> +
> +	value ^= 0x800000;
> +
> +	for (i = 0; i < hx711_data->gain_pulse; i++)
> +		ret = hx711_cycle(hx711_data);
> +
> +	mutex_unlock(&hx711_data->lock);
> +
> +	return value;
> +}
> +
> +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);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		switch (chan->type) {
> +		case IIO_VOLTAGE:
> +			*val = hx711_read(hx711_data);
> +			return IIO_VAL_INT;
> +		default:
> +			return -EINVAL;
> +		}
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static ssize_t hx711_gain_show(struct device *dev,
> +				struct device_attribute *attr,
> +				char *buf)
> +{
> +	struct hx711_data *hx711_data = iio_priv(dev_to_iio_dev(dev));
> +	int val;
> +
> +	switch (hx711_data->gain_pulse) {
> +	case HX711_GAIN_32:
> +		val = 32;
> +		break;
> +	case HX711_GAIN_64:
> +		val = 64;
> +		break;
> +	default:
> +		val = 128;
> +	}
> +
> +	return sprintf(buf, "%d\n", val);
> +}
> +
> +static ssize_t hx711_gain_store(struct device *dev,
> +				struct device_attribute *attr,
> +				const char *buf, size_t len)
> +{
> +	struct hx711_data *hx711_data = iio_priv(dev_to_iio_dev(dev));
> +	int ret, val;
> +	int gain_save = hx711_data->gain_pulse;
> +
> +	ret = kstrtoint((const char *) buf, 10, &val);
> +	if (ret)
> +		return -EINVAL;
> +
> +	switch (val) {
> +	case 32:
> +		hx711_data->gain_pulse = HX711_GAIN_32;
> +		break;
> +	case 64:
> +		hx711_data->gain_pulse = HX711_GAIN_64;
> +		break;
> +	case 128:
> +		hx711_data->gain_pulse = HX711_GAIN_128;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	dev_dbg(hx711_data->dev, "gain_pulse: %d\n", hx711_data->gain_pulse);
> +
> +	/* if gain has changed do a fake read for the new gain to be set
> +	 *   for the next read
> +	 */
> +	if (gain_save != hx711_data->gain_pulse)
> +		hx711_read(hx711_data);
> +
> +	return len;
> +}
> +
> +static IIO_DEVICE_ATTR(gain, S_IRUGO | S_IWUSR,
> +	hx711_gain_show, hx711_gain_store, 0);
> +
> +static struct attribute *hx711_attributes[] = {
> +	&iio_dev_attr_gain.dev_attr.attr,
> +	NULL,
> +};
> +
As Lars suggested, please use standard ABI (easier if you use the info_mask
elements and do it through read raw...
> +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,
> +	.attrs			= &hx711_attribute_group,
> +};
> +
> +static const struct iio_chan_spec hx711_chan_spec[] = {
> +	{
new line here is slightly nicer to read.
>.type = IIO_VOLTAGE,
> +		.info_mask_separate =
> +			BIT(IIO_CHAN_INFO_RAW),
> +	},
> +};
> +
> +static int hx711_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct hx711_data *hx711_data = NULL;
> +	struct iio_dev *iio;
> +	int ret = 0;
> +
> +	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);
> +
> +	hx711_data->gpiod_sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_HIGH);
> +	if (IS_ERR(hx711_data->gpiod_sck)) {
> +		dev_err(dev, "failed to get sck-gpiod: err=%ld\n",
> +					PTR_ERR(hx711_data->gpiod_sck));
> +		return PTR_ERR(hx711_data->gpiod_sck);
> +	}
> +
> +	hx711_data->gpiod_dout = devm_gpiod_get(dev, "dout", GPIOD_OUT_HIGH);
If there is a reason for getting an input as an output then it wants a comment!
> +	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);
> +	}
> +
> +	ret = gpiod_direction_input(hx711_data->gpiod_dout);
> +	if (ret < 0) {
> +		dev_err(hx711_data->dev, "gpiod_direction_input: %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = gpiod_direction_output(hx711_data->gpiod_sck, 0);
Doesn't the flag above already mean we are in output mode for this pin?
> +	if (ret < 0) {
> +		dev_err(hx711_data->dev, "gpiod_direction_output: %d\n", ret);
> +		return ret;
> +	}
> +
> +	platform_set_drvdata(pdev, iio);
> +
> +	iio->name = pdev->name;
> +	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);
> +}
> +
> +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,
> +	.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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