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SubjectRe: [PATCH 3/3] iio: wrapper: unit-converter: new driver
On Mon, 19 Mar 2018 18:02:46 +0100
Peter Rosin <peda@axentia.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 it too big for the ADC to handle.
> Likewise, if an ADC channel measures the voltage across a 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@axentia.se>
A few comments inline, but basically the code looks fine, just questions
around naming and bindings to answer.

Thanks,

Jonathan

> ---
> MAINTAINERS | 1 +
> drivers/iio/wrapper/Kconfig | 9 ++
> drivers/iio/wrapper/Makefile | 1 +
> drivers/iio/wrapper/iio-unit-converter.c | 268 +++++++++++++++++++++++++++++++
> 4 files changed, 279 insertions(+)
> create mode 100644 drivers/iio/wrapper/iio-unit-converter.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 5dd555c7b1b0..b879289f1318 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6889,6 +6889,7 @@ M: Peter Rosin <peda@axentia.se>
> L: linux-iio@vger.kernel.org
> S: Maintained
> F: Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt
> +F: drivers/iio/wrapper/iio-unit-converter.c
>
> IKANOS/ADI EAGLE ADSL USB DRIVER
> M: Matthieu Castet <castet.matthieu@free.fr>
> diff --git a/drivers/iio/wrapper/Kconfig b/drivers/iio/wrapper/Kconfig
> index f27de347c9b3..16554479264a 100644
> --- a/drivers/iio/wrapper/Kconfig
> +++ b/drivers/iio/wrapper/Kconfig
> @@ -15,4 +15,13 @@ config IIO_MUX
> To compile this driver as a module, choose M here: the
> module will be called iio-mux.
>
> +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.
> +
> + To compile this driver as a module, choose M here: the
> + module will be called iio-unit-converter.
> +
> endmenu
> diff --git a/drivers/iio/wrapper/Makefile b/drivers/iio/wrapper/Makefile
> index 53a7b78734e3..1b9db53bd420 100644
> --- a/drivers/iio/wrapper/Makefile
> +++ b/drivers/iio/wrapper/Makefile
> @@ -4,3 +4,4 @@
>
> # When adding new entries keep the list in alphabetical order
> obj-$(CONFIG_IIO_MUX) += iio-mux.o
> +obj-$(CONFIG_IIO_UNIT_CONVERTER) += iio-unit-converter.o
> diff --git a/drivers/iio/wrapper/iio-unit-converter.c b/drivers/iio/wrapper/iio-unit-converter.c
> new file mode 100644
> index 000000000000..53c126f39e4e
> --- /dev/null
> +++ b/drivers/iio/wrapper/iio-unit-converter.c
> @@ -0,0 +1,268 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * IIO unit converter
> + *
> + * Copyright (C) 2018 Axentia Technologies AB
> + *
> + * Author: Peter Rosin <peda@axentia.se>
> + */
> +
> +#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/property.h>
> +
> +struct unit_converter {
> + struct iio_channel *parent;
> + struct iio_dev *indio_dev;
> + 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->parent, val);
> +
> + case IIO_CHAN_INFO_SCALE:
> + ret = iio_read_channel_scale(uc->parent, 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;
> + }
> + return -EOPNOTSUPP;
Slightly clearer and less likely to give warningss from static checkers
if you put that return in a 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->parent, vals, length);
> + }
> +
> + return -EINVAL;
> +}
> +
> +static int unit_converter_write_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);
> +
> + switch (mask) {
> + case IIO_CHAN_INFO_RAW:
> + return iio_write_channel_raw(uc->parent, val);
Talk me through the logic of having this... Supporting a DAC?
Bindings don't talk about that possibility...

> + }
> +
> + return -EINVAL;
> +}
> +
> +static const struct iio_info unit_converter_info = {
> + .read_raw = unit_converter_read_raw,
> + .read_avail = unit_converter_read_avail,
> + .write_raw = unit_converter_write_raw,
> +};
> +
> +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->parent,
> + 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->parent,
> + uc->ext_info[private].name,
> + buf, len);
> +}
> +
> +static int unit_converter_configure_channel(struct device *dev,
> + struct unit_converter *uc,
> + enum iio_chan_type type)
> +{
> + struct iio_chan_spec *chan = &uc->chan;
> + struct iio_chan_spec const *pchan = uc->parent->channel;
> + int ret;
> +
> + chan->indexed = 1;
> + chan->output = pchan->output;
> + chan->ext_info = uc->ext_info;
> +
> + if (type == -1) {
> + ret = iio_get_channel_type(uc->parent, &type);
> + if (ret < 0) {
> + dev_err(dev, "failed to get parent channel type\n");
> + return ret;
> + }
> + }
> + chan->type = type;
> +
> + if (iio_channel_has_info(pchan, IIO_CHAN_INFO_RAW))
> + chan->info_mask_separate |= BIT(IIO_CHAN_INFO_RAW);
if the parent doesn't support RAW, is there a lot of point in carrying on?

> + if (iio_channel_has_info(pchan, IIO_CHAN_INFO_SCALE))
> + chan->info_mask_separate |= BIT(IIO_CHAN_INFO_SCALE);
> +
> + if (iio_channel_has_available(pchan, IIO_CHAN_INFO_RAW))
> + chan->info_mask_separate_available |= BIT(IIO_CHAN_INFO_RAW);
> +
> + chan->channel = 0;
> +
> + return 0;
> +}
> +
> +static int unit_converter_probe(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + struct iio_dev *indio_dev;
> + struct iio_channel *parent;
> + struct unit_converter *uc;
> + const char *type_name;
> + enum iio_chan_type type = -1; /* default to same as parent */
> + int sizeof_ext_info;
> + int sizeof_priv;
> + int i;
> + int ret;
> +
> + if (!device_property_read_string(dev, "type", &type_name)) {
> + if (!strcmp(type_name, "voltage"))
> + type = IIO_VOLTAGE;
> + else if (!strcmp(type_name, "current"))
> + type = IIO_CURRENT;
> + else
> + return -EINVAL;
> + }
> +
> + parent = devm_iio_channel_get(dev, "parent");
> + if (IS_ERR(parent)) {
> + if (PTR_ERR(parent) != -EPROBE_DEFER)
> + dev_err(dev, "failed to get parent channel\n");
> + return PTR_ERR(parent);
> + }
> +
> + sizeof_ext_info = iio_get_channel_ext_info_count(parent);
> + 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->numerator = 1;
> + uc->denominator = 1;
> + device_property_read_u32(dev, "numerator", &uc->numerator);
> + device_property_read_u32(dev, "denominator", &uc->denominator);
> + if (!uc->numerator || !uc->denominator) {
> + dev_err(dev, "invalid scaling factor.\n");
> + return -EINVAL;
> + }
> +
> + platform_set_drvdata(pdev, indio_dev);
> +
> + uc->parent = parent;
> +
> + 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,
> + parent->channel->ext_info,
> + sizeof_ext_info, GFP_KERNEL);
> + if (!uc->ext_info)
> + return -ENOMEM;
> +
> + for (i = 0; uc->ext_info[i].name; ++i) {
> + if (parent->channel->ext_info[i].read)
> + uc->ext_info[i].read = unit_converter_read_ext_info;
> + if (parent->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, type);
> + if (ret < 0)
> + return ret;
> +
> + ret = devm_iio_device_register(dev, indio_dev);
> + if (ret) {
> + dev_err(dev, "failed to register iio device\n");
> + return ret;
> + }
Drop the return out of the brackets and get rid of return 0 below.

> +
> + return 0;
> +}
> +
> +static const struct of_device_id unit_converter_match[] = {
> + { .compatible = "io-channel-unit-converter" },
> + { /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, unit_converter_match);
> +
> +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@axentia.se>");
> +MODULE_LICENSE("GPL v2");

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