Subject: Re: [PATCH v3 6/8] iio: dpot-dac: DAC driver based on a digital
 potentiometer
To: Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
        Jonathan Cameron <jic23@kernel.org>
References: <1477262381-7800-1-git-send-email-peda@axentia.se>
 <1477262381-7800-7-git-send-email-peda@axentia.se>
 <301ab064-cd90-d99d-a05a-8a50ba759c62@kernel.org>
 <alpine.DEB.2.02.1610301628400.32031@pmeerw.net>
CC: <linux-kernel@vger.kernel.org>, Hartmut Knaack <knaack.h@gmx.de>,
        Lars-Peter Clausen <lars@metafoo.de>, Rob Herring <robh+dt@kernel.org>,
        "Mark Rutland" <mark.rutland@arm.com>, <linux-iio@vger.kernel.org>,
        <devicetree@vger.kernel.org>
From: Peter Rosin <peda@axentia.se>
Organization: Axentia Technologies AB
Message-ID: <48f793af-6f70-d666-0e9e-c170e607ab7e@axentia.se>
Date: Sun, 30 Oct 2016 19:36:14 +0100
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On 2016-10-30 16:32, Peter Meerwald-Stadler wrote:
> On Sun, 30 Oct 2016, Jonathan Cameron wrote:
> 
>> On 23/10/16 23:39, Peter Rosin wrote:
>>> It is assumed that the dpot is used as a voltage divider between the
>>> current dpot wiper setting and the maximum resistance of the dpot. The
>>> divided voltage is provided by a vref regulator.
>>>
>>>                   .------.
>>>    .-----------.  |      |
>>>    | vref      |--'    .---.
>>>    | regulator |--.    |   |
>>>    '-----------'  |    | d |
>>>                   |    | p |
>>>                   |    | o |  wiper
>>>                   |    | t |<---------+
>>>                   |    |   |
>>>                   |    '---'       dac output voltage
>>>                   |      |
>>>                   '------+------------+
>>>
>>> Signed-off-by: Peter Rosin <peda@axentia.se>
>> Only a trivial suggestion to drop the devinfo about max ohms now it's
>> exposed (effectively) via the dpot driver. (really minor though so don't bother
>> respinning for that!)
>>
>> Jonathan
>>> ---
>>>  .../ABI/testing/sysfs-bus-iio-dac-dpot-dac         |   8 +
>>>  MAINTAINERS                                        |   2 +
>>>  drivers/iio/dac/Kconfig                            |  10 +
>>>  drivers/iio/dac/Makefile                           |   1 +
>>>  drivers/iio/dac/dpot-dac.c                         | 267 +++++++++++++++++++++
>>>  5 files changed, 288 insertions(+)
>>>  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-dac-dpot-dac
>>>  create mode 100644 drivers/iio/dac/dpot-dac.c
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-dac-dpot-dac b/Documentation/ABI/testing/sysfs-bus-iio-dac-dpot-dac
>>> new file mode 100644
>>> index 000000000000..580e93f373f6
>>> --- /dev/null
>>> +++ b/Documentation/ABI/testing/sysfs-bus-iio-dac-dpot-dac
>>> @@ -0,0 +1,8 @@
>>> +What:		/sys/bus/iio/devices/iio:deviceX/out_voltageY_raw_available
>>> +Date:		October 2016
>>> +KernelVersion:	4.9
>>> +Contact:	Peter Rosin <peda@axentia.se>
>>> +Description:
>>> +		The range of available values represented as the minimum value,
>>> +		the step and the maximum value, all enclosed in square brackets.
>>> +		Example: [0 1 256]
>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>> index 6218010128dc..d7375f45ff0f 100644
>>> --- a/MAINTAINERS
>>> +++ b/MAINTAINERS
>>> @@ -6115,7 +6115,9 @@ IIO DIGITAL POTENTIOMETER DAC
>>>  M:	Peter Rosin <peda@axentia.se>
>>>  L:	linux-iio@vger.kernel.org
>>>  S:	Maintained
>>> +F:	Documentation/ABI/testing/sysfs-bus-iio-dac-dpot-dac
>>>  F:	Documentation/devicetree/bindings/iio/dac/dpot-dac.txt
>>> +F:	drivers/iio/dac/dpot-dac.c
>>>  
>>>  IIO SUBSYSTEM AND DRIVERS
>>>  M:	Jonathan Cameron <jic23@kernel.org>
>>> diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
>>> index 120b24478469..d3084028905b 100644
>>> --- a/drivers/iio/dac/Kconfig
>>> +++ b/drivers/iio/dac/Kconfig
>>> @@ -200,6 +200,16 @@ config AD8801
>>>  	  To compile this driver as a module choose M here: the module will be called
>>>  	  ad8801.
>>>  
>>> +config DPOT_DAC
>>> +	tristate "DAC emulation using a DPOT"
>>> +	depends on OF
>>> +	help
>>> +	  Say yes here to build support for DAC emulation using a digital
>>> +	  potentiometer.
>>> +
>>> +	  To compile this driver as a module, choose M here: the module will be
>>> +	  called dpot-dac.
>>> +
>>>  config LPC18XX_DAC
>>>  	tristate "NXP LPC18xx DAC driver"
>>>  	depends on ARCH_LPC18XX || COMPILE_TEST
>>> diff --git a/drivers/iio/dac/Makefile b/drivers/iio/dac/Makefile
>>> index 27642bbf75f2..f01bf4a99867 100644
>>> --- a/drivers/iio/dac/Makefile
>>> +++ b/drivers/iio/dac/Makefile
>>> @@ -22,6 +22,7 @@ obj-$(CONFIG_AD5686) += ad5686.o
>>>  obj-$(CONFIG_AD7303) += ad7303.o
>>>  obj-$(CONFIG_AD8801) += ad8801.o
>>>  obj-$(CONFIG_CIO_DAC) += cio-dac.o
>>> +obj-$(CONFIG_DPOT_DAC) += dpot-dac.o
>>>  obj-$(CONFIG_LPC18XX_DAC) += lpc18xx_dac.o
>>>  obj-$(CONFIG_M62332) += m62332.o
>>>  obj-$(CONFIG_MAX517) += max517.o
>>> diff --git a/drivers/iio/dac/dpot-dac.c b/drivers/iio/dac/dpot-dac.c
>>> new file mode 100644
>>> index 000000000000..f227a211d34d
>>> --- /dev/null
>>> +++ b/drivers/iio/dac/dpot-dac.c
>>> @@ -0,0 +1,267 @@
>>> +/*
>>> + * IIO DAC emulation driver using a digital potentiometer
>>> + *
>>> + * Copyright (C) 2016 Axentia Technologies AB
>>> + *
>>> + * Author: Peter Rosin <peda@axentia.se>
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify
>>> + * it under the terms of the GNU General Public License version 2 as
>>> + * published by the Free Software Foundation.
>>> + */
>>> +
>>> +/*
>>> + * It is assumed that the dpot is used as a voltage divider between the
>>> + * current dpot wiper setting and the maximum resistance of the dpot. The
>>> + * divided voltage is provided by a vref regulator.
>>> + *
>>> + *                   .------.
>>> + *    .-----------.  |      |
>>> + *    | vref      |--'    .---.
>>> + *    | regulator |--.    |   |
>>> + *    '-----------'  |    | d |
>>> + *                   |    | p |
>>> + *                   |    | o |  wiper
>>> + *                   |    | t |<---------+
>>> + *                   |    |   |
>>> + *                   |    '---'       dac output voltage
>>> + *                   |      |
>>> + *                   '------+------------+
>>> + */
>>> +
>>> +#include <linux/err.h>
>>> +#include <linux/iio/consumer.h>
>>> +#include <linux/iio/iio.h>
>>> +#include <linux/module.h>
>>> +#include <linux/of.h>
>>> +#include <linux/platform_device.h>
>>> +#include <linux/regulator/consumer.h>
>>> +
>>> +struct dpot_dac {
>>> +	struct regulator *vref;
>>> +	struct iio_channel *dpot;
>>> +	u32 max_ohms;
>>> +};
>>> +
>>> +static const struct iio_chan_spec dpot_dac_iio_channel = {
>>> +	.type = IIO_VOLTAGE,
>>> +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW)
>>> +			    | BIT(IIO_CHAN_INFO_SCALE),
>>> +	.info_mask_separate_available = BIT(IIO_CHAN_INFO_RAW),
>>> +	.output = 1,
>>> +	.indexed = 1,
>>> +};
>>> +
>>> +static int dpot_dac_read_raw(struct iio_dev *indio_dev,
>>> +			     struct iio_chan_spec const *chan,
>>> +			     int *val, int *val2, long mask)
>>> +{
>>> +	struct dpot_dac *dac = iio_priv(indio_dev);
>>> +	int ret;
>>> +	unsigned long long tmp;
>>> +
>>> +	switch (mask) {
>>> +	case IIO_CHAN_INFO_RAW:
>>> +		return iio_read_channel_raw(dac->dpot, val);
>>> +
>>> +	case IIO_CHAN_INFO_SCALE:
>>> +		ret = iio_read_channel_scale(dac->dpot, val, val2);
>>> +		switch (ret) {
>>> +		case IIO_VAL_FRACTIONAL_LOG2:
>>> +			tmp = *val * 1000000000LL;
>>> +			do_div(tmp, dac->max_ohms);
>>> +			tmp *= regulator_get_voltage(dac->vref) / 1000;
>>> +			do_div(tmp, 1000000000LL);
>>> +			*val = tmp;
>>> +			return ret;
>>> +		case IIO_VAL_INT:
>>> +			/*
>>> +			 * Convert integer scale to fractional scale by
>>> +			 * setting the denominator (val2) to one...
>>> +			 */
>>> +			*val2 = 1;
>>> +			ret = IIO_VAL_FRACTIONAL;
>>> +			/* ...and fall through. */
>>> +		case IIO_VAL_FRACTIONAL:
>>> +			*val *= regulator_get_voltage(dac->vref) / 1000;
>>> +			*val2 *= dac->max_ohms;
>>> +			break;
>>> +		}
>>> +
>>> +		return ret;
>>> +	}
>>> +
>>> +	return -EINVAL;
>>> +}
>>> +
>>> +static int dpot_dac_read_avail(struct iio_dev *indio_dev,
>>> +			       struct iio_chan_spec const *chan,
>>> +			       const int **vals, int *type, int *length,
>>> +			       long mask)
>>> +{
>>> +	struct dpot_dac *dac = iio_priv(indio_dev);
>>> +
>>> +	switch (mask) {
>>> +	case IIO_CHAN_INFO_RAW:
>>> +		return iio_read_avail_channel_raw(dac->dpot,
>>> +						  vals, type, length);
>>> +	}
>>> +
>>> +	return -EINVAL;
>>> +}
>>> +
>>> +static int dpot_dac_write_raw(struct iio_dev *indio_dev,
>>> +			      struct iio_chan_spec const *chan,
>>> +			      int val, int val2, long mask)
>>> +{
>>> +	struct dpot_dac *dac = iio_priv(indio_dev);
>>> +
>>> +	switch (mask) {
>>> +	case IIO_CHAN_INFO_RAW:
>>> +		return iio_write_channel_raw(dac->dpot, val);
>>> +	}
>>> +
>>> +	return -EINVAL;
>>> +}
>>> +
>>> +static const struct iio_info dpot_dac_info = {
>>> +	.read_raw = dpot_dac_read_raw,
>>> +	.read_avail = dpot_dac_read_avail,
>>> +	.write_raw = dpot_dac_write_raw,
>>> +	.driver_module = THIS_MODULE,
>>> +};
>>> +
>>> +static int dpot_dac_channel_max_ohms(struct iio_dev *indio_dev)
>>> +{
>>> +	struct device *dev = &indio_dev->dev;
>>> +	struct dpot_dac *dac = iio_priv(indio_dev);
>>> +	unsigned long long tmp;
>>> +	int ret;
>>> +	int val;
>>> +	int val2;
>>> +	int max;
>>> +
>>> +	ret = iio_read_max_channel_raw(dac->dpot, &max);
>>> +	if (ret < 0) {
>>> +		dev_err(dev, "dpot does not indicate its raw maximum value\n");
>>> +		return ret;
>>> +	}
>>> +
>>> +	switch (iio_read_channel_scale(dac->dpot, &val, &val2)) {
>>> +	case IIO_VAL_INT:
>>> +		return max * val;
>>> +	case IIO_VAL_FRACTIONAL:
>>> +		tmp = (unsigned long long)max * val;
>>> +		do_div(tmp, val2);
>>> +		return tmp;
>>> +	case IIO_VAL_FRACTIONAL_LOG2:
>>> +		tmp = (s64)val * 1000000000LL * max >> val2;
> 
> (s64) necessary?
> or rather unsigned long long?

Fuck it, I'll just remove that case completely. I don't care about
weird fractional-log2-shit that'll probably overflow anyway. Happy?

>>> +		do_div(tmp, 1000000000LL);
>>> +		return tmp;
>>> +	default:
>>> +		dev_err(dev, "dpot has a scale that is too weird\n");
>>> +	}
>>> +
>>> +	return -EINVAL;
>>> +}
>>> +
>>> +static int dpot_dac_probe(struct platform_device *pdev)
>>> +{
>>> +	struct device *dev = &pdev->dev;
>>> +	struct iio_dev *indio_dev;
>>> +	struct dpot_dac *dac;
>>> +	enum iio_chan_type type;
>>> +	int ret;
>>> +
>>> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*dac));
>>> +	if (!indio_dev)
>>> +		return -ENOMEM;
>>> +
>>> +	platform_set_drvdata(pdev, indio_dev);
>>> +	dac = iio_priv(indio_dev);
>>> +
>>> +	indio_dev->name = dev_name(dev);
>>> +	indio_dev->dev.parent = dev;
>>> +	indio_dev->info = &dpot_dac_info;
>>> +	indio_dev->modes = INDIO_DIRECT_MODE;
>>> +	indio_dev->channels = &dpot_dac_iio_channel;
>>> +	indio_dev->num_channels = 1;
>>> +
>>> +	dac->vref = devm_regulator_get(dev, "vref");
>>> +	if (IS_ERR(dac->vref)) {
>>> +		if (PTR_ERR(dac->dpot) != -EPROBE_DEFER)
>>> +			dev_err(&pdev->dev, "failed to get vref regulator\n");
>>> +		return PTR_ERR(dac->vref);
>>> +	}
>>> +
>>> +	dac->dpot = devm_iio_channel_get(dev, "dpot");
>>> +	if (IS_ERR(dac->dpot)) {
>>> +		if (PTR_ERR(dac->dpot) != -EPROBE_DEFER)
>>> +			dev_err(dev, "failed to get dpot input channel\n");
>>> +		return PTR_ERR(dac->dpot);
>>> +	}
>>> +
>>> +	ret = iio_get_channel_type(dac->dpot, &type);
>>> +	if (ret < 0)
>>> +		return ret;
>>> +
>>> +	if (type != IIO_RESISTANCE) {
>>> +		dev_err(dev, "dpot is of the wrong type\n");
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +	ret = dpot_dac_channel_max_ohms(indio_dev);
>>> +	if (ret < 0)
>>> +		return ret;
>>> +	dac->max_ohms = ret;
>>> +	dev_info(dev, "dpot max is %d\n", dac->max_ohms);
>> Given we can query this (indirectly) from the dpot itself, I'd drop this now.
> 
> max_ohms is u32, so this should be %u not %d?

You're right, but that dev_info is about to be killed anyway,
as requested by Jonathan.

Cheers,
Peter

>>
>>> +
>>> +	ret = regulator_enable(dac->vref);
>>> +	if (ret) {
>>> +		dev_err(dev, "failed to enable the vref regulator\n");
>>> +		return ret;
>>> +	}
>>> +
>>> +	ret = iio_device_register(indio_dev);
>>> +	if (ret) {
>>> +		dev_err(dev, "failed to register iio device\n");
>>> +		goto disable_reg;
>>> +	}
>>> +
>>> +	return 0;
>>> +
>>> +disable_reg:
>>> +	regulator_disable(dac->vref);
>>> +	return ret;
>>> +}
>>> +
>>> +static int dpot_dac_remove(struct platform_device *pdev)
>>> +{
>>> +	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
>>> +	struct dpot_dac *dac = iio_priv(indio_dev);
>>> +
>>> +	iio_device_unregister(indio_dev);
>>> +	regulator_disable(dac->vref);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static const struct of_device_id dpot_dac_match[] = {
>>> +	{ .compatible = "dpot-dac" },
>>> +	{ /* sentinel */ }
>>> +};
>>> +MODULE_DEVICE_TABLE(of, dpot_dac_match);
>>> +
>>> +static struct platform_driver dpot_dac_driver = {
>>> +	.probe = dpot_dac_probe,
>>> +	.remove = dpot_dac_remove,
>>> +	.driver = {
>>> +		.name = "iio-dpot-dac",
>>> +		.of_match_table = dpot_dac_match,
>>> +	},
>>> +};
>>> +module_platform_driver(dpot_dac_driver);
>>> +
>>> +MODULE_DESCRIPTION("DAC emulation driver using a digital potentiometer");
>>> +MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
>>> +MODULE_LICENSE("GPL v2");
>>>
>>
>