Re: [PATCH v3 6/8] iio: dpot-dac: DAC driver based on a digital potentiometer

From: Peter Rosin
Date: Sun Oct 30 2016 - 15:08:35 EST

On 2016-10-30 16:32, Peter Meerwald-Stadler wrote:
> 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@xxxxxxxxxx>
>> 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@xxxxxxxxxx>
>>> +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@xxxxxxxxxx>
>>> L: linux-iio@xxxxxxxxxxxxxxx
>>> 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@xxxxxxxxxx>
>>> 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@xxxxxxxxxx>
>>> + *
>>> + * 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?

Fuck it, I'll just remove that case completely. I don't care about
weird fractional-log2-shit that'll probably overflow anyway. Happy?

>>> + 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?

You're right, but that dev_info is about to be killed anyway,
as requested by Jonathan.

Cheers,
Peter

>>
>>> +
>>> + 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@xxxxxxxxxx>");
>>> +MODULE_LICENSE("GPL v2");
>>>
>>
>