[PATCH v4 6/8] iio: dpot-dac: DAC driver based on a digital potentiometer

Peter Rosin
2016-11-08T19:36:44Z

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>
---
.../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 | 266 +++++++++++++++++++++
5 files changed, 287 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@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]
diff --git a/MAINTAINERS b/MAINTAINERS
index 4ff9c12b1313..583c6c93b6f3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6128,7 +6128,9 @@ 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>
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..eb1f0509a3ec
--- /dev/null
+++ b/drivers/iio/dac/dpot-dac.c
@@ -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->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;
+
+ 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");
--
2.1.4