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iio: dpot-dac: DAC driver based on a digital potentiometer 

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>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
This commit is contained in:
Peter Rosin 2016-11-08 12:58:56 +01:00 committed by Jonathan Cameron
parent ed13134ba8
commit 7fde1484af
5 changed files with 287 additions and 0 deletions
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8
Documentation/ABI/testing/sysfs-bus-iio-dac-dpot-dac Normal file
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@ -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]

2
MAINTAINERS
View File

@ -6123,7 +6123,9 @@ 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>

10
drivers/iio/dac/Kconfig
View File

@ -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

1
drivers/iio/dac/Makefile
View File

@ -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

266
drivers/iio/dac/dpot-dac.c Normal file
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@ -0,0 +1,266 @@
/*
* 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:
*type = IIO_VAL_INT;
return iio_read_avail_channel_raw(dac->dpot, vals, 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 = val * 1000000000LL * max >> val2;
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->vref) != -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;
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");