Date:   Sun, 15 Apr 2018 18:31:40 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Peter Rosin <peda@...ntia.se>
Cc:     linux-kernel@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Andrew F . Davis" <afd@...com>,
        Fabio Estevam <festevam@...il.com>, linux-iio@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v3 2/2] iio: afe: unit-converter: new driver

On Tue, 10 Apr 2018 17:28:02 +0200
Peter Rosin <peda@...ntia.se> wrote:

> If an ADC channel measures the midpoint of a voltage divider, the
> interesting voltage is often the voltage over the full resistance.
> E.g. if the full voltage is too big for the ADC to handle.
> Likewise, if an ADC channel measures the voltage across a shunt
> resistor, the interesting value is often the current through the
> resistor.
> 
> This driver solves both problems by allowing to linearly scale a channel
> and by allowing changes to the type of the channel. Or both.
> 
> Signed-off-by: Peter Rosin <peda@...ntia.se>
So I 'think' the only outstanding question is Andrew's one about the driver
name.  We aren't in a hurry at this point in the kernel cycle, so lets
wait until that discussion has ended.  Assuming that we do possibly end
up with a change, then please roll all the patches up into a single series
to avoid me getting confusion.

Thanks,

Jonathan

> ---
>  MAINTAINERS                          |   1 +
>  drivers/iio/Kconfig                  |   1 +
>  drivers/iio/Makefile                 |   1 +
>  drivers/iio/afe/Kconfig              |  18 +++
>  drivers/iio/afe/Makefile             |   6 +
>  drivers/iio/afe/iio-unit-converter.c | 291 +++++++++++++++++++++++++++++++++++
>  6 files changed, 318 insertions(+)
>  create mode 100644 drivers/iio/afe/Kconfig
>  create mode 100644 drivers/iio/afe/Makefile
>  create mode 100644 drivers/iio/afe/iio-unit-converter.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 237fcdfdddc6..d2a28b915fca 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6893,6 +6893,7 @@ L:	linux-iio@...r.kernel.org
>  S:	Maintained
>  F:	Documentation/devicetree/bindings/iio/afe/current-sense-shunt.txt
>  F:	Documentation/devicetree/bindings/iio/afe/voltage-divider.txt
> +F:	drivers/iio/afe/iio-unit-converter.c
>  
>  IKANOS/ADI EAGLE ADSL USB DRIVER
>  M:	Matthieu Castet <castet.matthieu@...e.fr>
> diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
> index b3c8c6ef0dff..d69e85a8bdc3 100644
> --- a/drivers/iio/Kconfig
> +++ b/drivers/iio/Kconfig
> @@ -70,6 +70,7 @@ config IIO_TRIGGERED_EVENT
>  
>  source "drivers/iio/accel/Kconfig"
>  source "drivers/iio/adc/Kconfig"
> +source "drivers/iio/afe/Kconfig"
>  source "drivers/iio/amplifiers/Kconfig"
>  source "drivers/iio/chemical/Kconfig"
>  source "drivers/iio/common/Kconfig"
> diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
> index b16b2e9ddc40..d8cba9c229c0 100644
> --- a/drivers/iio/Makefile
> +++ b/drivers/iio/Makefile
> @@ -15,6 +15,7 @@ obj-$(CONFIG_IIO_TRIGGERED_EVENT) += industrialio-triggered-event.o
>  
>  obj-y += accel/
>  obj-y += adc/
> +obj-y += afe/
>  obj-y += amplifiers/
>  obj-y += buffer/
>  obj-y += chemical/
> diff --git a/drivers/iio/afe/Kconfig b/drivers/iio/afe/Kconfig
> new file mode 100644
> index 000000000000..642ce4eb12a6
> --- /dev/null
> +++ b/drivers/iio/afe/Kconfig
> @@ -0,0 +1,18 @@
> +#
> +# Analog Front End drivers
> +#
> +# When adding new entries keep the list in alphabetical order
> +
> +menu "Analog Front Ends"
> +
> +config IIO_UNIT_CONVERTER
> +	tristate "IIO unit converter"
> +	depends on OF || COMPILE_TEST
> +	help
> +	  Say yes here to build support for the IIO unit converter
> +	  that handles voltage dividers and current sense shunts.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called iio-unit-converter.
> +
> +endmenu
> diff --git a/drivers/iio/afe/Makefile b/drivers/iio/afe/Makefile
> new file mode 100644
> index 000000000000..7691cc5b809a
> --- /dev/null
> +++ b/drivers/iio/afe/Makefile
> @@ -0,0 +1,6 @@
> +#
> +# Makefile for industrial I/O Analog Front Ends (AFE)
> +#
> +
> +# When adding new entries keep the list in alphabetical order
> +obj-$(CONFIG_IIO_UNIT_CONVERTER) += iio-unit-converter.o
> diff --git a/drivers/iio/afe/iio-unit-converter.c b/drivers/iio/afe/iio-unit-converter.c
> new file mode 100644
> index 000000000000..fc50290d7e5e
> --- /dev/null
> +++ b/drivers/iio/afe/iio-unit-converter.c
> @@ -0,0 +1,291 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * IIO unit converter
> + *
> + * Copyright (C) 2018 Axentia Technologies AB
> + *
> + * Author: Peter Rosin <peda@...ntia.se>
> + */
> +
> +#include <linux/err.h>
> +#include <linux/gcd.h>
> +#include <linux/iio/consumer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/property.h>
> +
> +struct unit_converter;
> +
> +struct unit_converter_cfg {
> +	enum iio_chan_type type;
> +	int (*props)(struct device *dev, struct unit_converter *uc);
> +};
> +
> +struct unit_converter {
> +	const struct unit_converter_cfg *cfg;
> +	struct iio_channel *source;
> +	struct iio_chan_spec chan;
> +	struct iio_chan_spec_ext_info *ext_info;
> +	s32 numerator;
> +	s32 denominator;
> +};
> +
> +static int unit_converter_read_raw(struct iio_dev *indio_dev,
> +				   struct iio_chan_spec const *chan,
> +				   int *val, int *val2, long mask)
> +{
> +	struct unit_converter *uc = iio_priv(indio_dev);
> +	unsigned long long tmp;
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		return iio_read_channel_raw(uc->source, val);
> +
> +	case IIO_CHAN_INFO_SCALE:
> +		ret = iio_read_channel_scale(uc->source, val, val2);
> +		switch (ret) {
> +		case IIO_VAL_FRACTIONAL:
> +			*val *= uc->numerator;
> +			*val2 *= uc->denominator;
> +			return ret;
> +		case IIO_VAL_INT:
> +			*val *= uc->numerator;
> +			if (uc->denominator == 1)
> +				return ret;
> +			*val2 = uc->denominator;
> +			return IIO_VAL_FRACTIONAL;
> +		case IIO_VAL_FRACTIONAL_LOG2:
> +			tmp = *val * 1000000000LL;
> +			do_div(tmp, uc->denominator);
> +			tmp *= uc->numerator;
> +			do_div(tmp, 1000000000LL);
> +			*val = tmp;
> +			return ret;
> +		default:
> +			return -EOPNOTSUPP;
> +		}
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int unit_converter_read_avail(struct iio_dev *indio_dev,
> +				     struct iio_chan_spec const *chan,
> +				     const int **vals, int *type, int *length,
> +				     long mask)
> +{
> +	struct unit_converter *uc = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		*type = IIO_VAL_INT;
> +		return iio_read_avail_channel_raw(uc->source, vals, length);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct iio_info unit_converter_info = {
> +	.read_raw = unit_converter_read_raw,
> +	.read_avail = unit_converter_read_avail,
> +};
> +
> +static ssize_t unit_converter_read_ext_info(struct iio_dev *indio_dev,
> +					    uintptr_t private,
> +					    struct iio_chan_spec const *chan,
> +					    char *buf)
> +{
> +	struct unit_converter *uc = iio_priv(indio_dev);
> +
> +	return iio_read_channel_ext_info(uc->source,
> +					 uc->ext_info[private].name,
> +					 buf);
> +}
> +
> +static ssize_t unit_converter_write_ext_info(struct iio_dev *indio_dev,
> +					     uintptr_t private,
> +					     struct iio_chan_spec const *chan,
> +					     const char *buf, size_t len)
> +{
> +	struct unit_converter *uc = iio_priv(indio_dev);
> +
> +	return iio_write_channel_ext_info(uc->source,
> +					  uc->ext_info[private].name,
> +					  buf, len);
> +}
> +
> +static int unit_converter_configure_channel(struct device *dev,
> +					    struct unit_converter *uc)
> +{
> +	struct iio_chan_spec *chan = &uc->chan;
> +	struct iio_chan_spec const *schan = uc->source->channel;
> +
> +	chan->indexed = 1;
> +	chan->output = schan->output;
> +	chan->ext_info = uc->ext_info;
> +	chan->type = uc->cfg->type;
> +
> +	if (!iio_channel_has_info(schan, IIO_CHAN_INFO_RAW) ||
> +	    !iio_channel_has_info(schan, IIO_CHAN_INFO_SCALE)) {
> +		dev_err(dev, "source channel does not support raw/scale\n");
> +		return -EINVAL;
> +	}
> +
> +	chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
> +		BIT(IIO_CHAN_INFO_SCALE);
> +
> +	if (iio_channel_has_available(schan, IIO_CHAN_INFO_RAW))
> +		chan->info_mask_separate_available |= BIT(IIO_CHAN_INFO_RAW);
> +
> +	return 0;
> +}
> +
> +static int unit_converter_current_sense_shunt_props(struct device *dev,
> +						    struct unit_converter *uc)
> +{
> +	u32 shunt;
> +	u32 factor;
> +	int ret;
> +
> +	ret = device_property_read_u32(dev, "shunt-resistor-micro-ohms",
> +				       &shunt);
> +	if (ret) {
> +		dev_err(dev, "failed to read the shunt resistance: %d\n", ret);
> +		return ret;
> +	}
> +
> +	factor = gcd(shunt, 1000000);
> +	uc->numerator = 1000000 / factor;
> +	uc->denominator = shunt / factor;
> +
> +	return 0;
> +}
> +
> +static int unit_converter_voltage_divider_props(struct device *dev,
> +						struct unit_converter *uc)
> +{
> +	device_property_read_u32(dev, "numerator", &uc->numerator);
> +	device_property_read_u32(dev, "denominator", &uc->denominator);
> +
> +	return 0;
> +}
> +
> +enum unit_converter_variant {
> +	CURRENT_SENSE_SHUNT,
> +	VOLTAGE_DIVIDER,
> +};
> +
> +static const struct unit_converter_cfg unit_converter_cfg[] = {
> +	[CURRENT_SENSE_SHUNT] = {
> +		.type = IIO_CURRENT,
> +		.props = unit_converter_current_sense_shunt_props,
> +	},
> +	[VOLTAGE_DIVIDER] = {
> +		.type = IIO_VOLTAGE,
> +		.props = unit_converter_voltage_divider_props,
> +	},
> +};
> +
> +static const struct of_device_id unit_converter_match[] = {
> +	{ .compatible = "current-sense-shunt",
> +	  .data = &unit_converter_cfg[CURRENT_SENSE_SHUNT], },
> +	{ .compatible = "voltage-divider",
> +	  .data = &unit_converter_cfg[VOLTAGE_DIVIDER], },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, unit_converter_match);
> +
> +static int unit_converter_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct iio_dev *indio_dev;
> +	struct iio_channel *source;
> +	struct unit_converter *uc;
> +	int sizeof_ext_info;
> +	int sizeof_priv;
> +	int i;
> +	int ret;
> +
> +	source = devm_iio_channel_get(dev, NULL);
> +	if (IS_ERR(source)) {
> +		if (PTR_ERR(source) != -EPROBE_DEFER)
> +			dev_err(dev, "failed to get source channel\n");
> +		return PTR_ERR(source);
> +	}
> +
> +	sizeof_ext_info = iio_get_channel_ext_info_count(source);
> +	if (sizeof_ext_info) {
> +		sizeof_ext_info += 1; /* one extra entry for the sentinel */
> +		sizeof_ext_info *= sizeof(*uc->ext_info);
> +	}
> +
> +	sizeof_priv = sizeof(*uc) + sizeof_ext_info;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof_priv);
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	uc = iio_priv(indio_dev);
> +
> +	uc->cfg = of_device_get_match_data(dev);
> +	uc->numerator = 1;
> +	uc->denominator = 1;
> +
> +	ret = uc->cfg->props(dev, uc);
> +	if (ret)
> +		return ret;
> +
> +	if (!uc->numerator || !uc->denominator) {
> +		dev_err(dev, "invalid scaling factor.\n");
> +		return -EINVAL;
> +	}
> +
> +	platform_set_drvdata(pdev, indio_dev);
> +
> +	uc->source = source;
> +
> +	indio_dev->name = dev_name(dev);
> +	indio_dev->dev.parent = dev;
> +	indio_dev->info = &unit_converter_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = &uc->chan;
> +	indio_dev->num_channels = 1;
> +	if (sizeof_ext_info) {
> +		uc->ext_info = devm_kmemdup(dev,
> +					    source->channel->ext_info,
> +					    sizeof_ext_info, GFP_KERNEL);
> +		if (!uc->ext_info)
> +			return -ENOMEM;
> +
> +		for (i = 0; uc->ext_info[i].name; ++i) {
> +			if (source->channel->ext_info[i].read)
> +				uc->ext_info[i].read = unit_converter_read_ext_info;
> +			if (source->channel->ext_info[i].write)
> +				uc->ext_info[i].write = unit_converter_write_ext_info;
> +			uc->ext_info[i].private = i;
> +		}
> +	}
> +
> +	ret = unit_converter_configure_channel(dev, uc);
> +	if (ret)
> +		return ret;
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}
> +
> +static struct platform_driver unit_converter_driver = {
> +	.probe = unit_converter_probe,
> +	.driver = {
> +		.name = "iio-unit-converter",
> +		.of_match_table = unit_converter_match,
> +	},
> +};
> +module_platform_driver(unit_converter_driver);
> +
> +MODULE_DESCRIPTION("IIO unit converter driver");
> +MODULE_AUTHOR("Peter Rosin <peda@...ntia.se>");
> +MODULE_LICENSE("GPL v2");

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