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Date: Sun, 30 Oct 2016 16:32:39 +0100 (CET)
From: Peter Meerwald-Stadler <pmeerw@...erw.net>
To: Jonathan Cameron <jic23@...nel.org>, Peter Rosin <peda@...ntia.se>
cc: linux-kernel@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
Lars-Peter Clausen <lars@...afoo.de>,
Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>, linux-iio@...r.kernel.org,
devicetree@...r.kernel.org
Subject: Re: [PATCH v3 6/8] iio: dpot-dac: DAC driver based on a digital
potentiometer
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@...ntia.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@...ntia.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@...ntia.se>
> > L: linux-iio@...r.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@...nel.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@...ntia.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?
> > + 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?
>
> > +
> > + 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@...ntia.se>");
> > +MODULE_LICENSE("GPL v2");
> >
>
--
Peter Meerwald-Stadler
+43-664-2444418 (mobile)
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