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SubjectRe: [PATCH 2/4] iio: dpot-dac: DAC driver based on a digital potentiometer

> It is assumed the 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
> | |
> '------+------------+

nice ASCII art :)
comments below, just nitpicking

> Signed-off-by: Peter Rosin <peda@axentia.se>
> ---
> MAINTAINERS | 1 +
> drivers/iio/dac/Kconfig | 10 +++
> drivers/iio/dac/Makefile | 1 +
> drivers/iio/dac/dpot-dac.c | 219 +++++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 231 insertions(+)
> create mode 100644 drivers/iio/dac/dpot-dac.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index c68b72088945..8c8aae24b96b 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6116,6 +6116,7 @@ M: Peter Rosin <peda@axentia.se>
> L: linux-iio@vger.kernel.org
> S: Maintained
> 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..934d4138fcdb 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 iio-dpot-dac.

I guess the name will be 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..94fbb4b27287
> --- /dev/null
> +++ b/drivers/iio/dac/dpot-dac.c
> @@ -0,0 +1,219 @@
> +/*
> + * 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 the that the dpot is used as a voltage divider between the

delete first 'the'

> + * current dpot wiper setting and the maximum resistance of the dpot. The
> + * divided voltage is provided by a vref regulator.
> + *
> + * .------.
> + * .-----------. | |
> + * | Vref |--' .---.

vref maybe lowercase

> + * | 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;

const

> + 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),
> + .output = 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;

s64 (which is used to cast below)

> +
> + 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 = (s64)*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:
> + *val2 = 1;

I think this needs a comment to clarify what's going on...

> + ret = IIO_VAL_FRACTIONAL;
> + break;
> + }
> + *val *= regulator_get_voltage(dac->vref) / 1000;
> + *val2 *= dac->max_ohms;
> +
> + return ret;
> + }
> +
> + 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,
> + .write_raw = dpot_dac_write_raw,
> + .driver_module = THIS_MODULE,
> +};
> +
> +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;

maybe ARRAY_SIZE(dpot_dac_iio_channel) to future-proof it

> +
> + 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);
> + }
> +
> + switch (iio_read_channel_scale(dac->dpot, &ret, NULL)) {
> + case IIO_VAL_INT:
> + case IIO_VAL_FRACTIONAL:
> + case IIO_VAL_FRACTIONAL_LOG2:
> + break;
> + default:
> + dev_err(dev, "dpot has a scale that is too weird\n");

:-)

> + return -EINVAL;
> + }
> +
> + 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 = of_property_read_u32(dev->of_node, "dpot-dac,max-ohms",
> + &dac->max_ohms);
> + if (ret) {
> + dev_err(dev, "the dpot-dac,max-ohms property is missing\n");
> + return ret;
> + }
> +
> + 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");
>

--

Peter Meerwald-Stadler
+43-664-2444418 (mobile)

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