Re: [PATCHv2] iio: adc: Add Maxim MAX11100 driver

[Jonathan Cameron <jic23@kernel.org>]

On 02/01/17 09:19, jacopo mondi wrote:
> Hi Jonathan,
>    thanks for review
> 
> On 30/12/2016 17:31, Jonathan Cameron wrote:
>> On 14/12/16 12:00, jacopo@jmondi.org wrote:
>>> Hello Peter,
>>>    thanks for review
>>>
>>> On 13/12/2016 21:33, Peter Meerwald-Stadler wrote:
>>>>
>>>>> Add IIO driver for Maxim MAX11100 single-channel ADC.
>>>>> Add DT bindings documentation.
>>>>
>>>> some more comments
>>>>
>>>>> Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
>>>>> ---
>>>>>
>>>>> v1 -> v2:
>>>>>     - incorporated pmeerw's review comments
>>>>>     - retrieve vref from dts and use that to convert read_raw result
>>>>>       to mV
>>>>>     - add device tree bindings documentation
>>>>>
>>>>> ---
>>>>>  .../devicetree/bindings/iio/adc/max11100.txt       |  17 +++
>>>>>  drivers/iio/adc/Kconfig                            |   9 ++
>>>>>  drivers/iio/adc/Makefile                           |   1 +
>>>>>  drivers/iio/adc/max11100.c                         | 166 +++++++++++++++++++++
>>>>>  4 files changed, 193 insertions(+)
>>>>>  create mode 100644 Documentation/devicetree/bindings/iio/adc/max11100.txt
>>>>>  create mode 100644 drivers/iio/adc/max11100.c
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/iio/adc/max11100.txt b/Documentation/devicetree/bindings/iio/adc/max11100.txt
>>>>> new file mode 100644
>>>>> index 0000000..6877c11
>>>>> --- /dev/null
>>>>> +++ b/Documentation/devicetree/bindings/iio/adc/max11100.txt
>>>>> @@ -0,0 +1,17 @@
>>>>> +* Maxim max11100 Analog to Digital Converter (ADC)
>>>>> +
>>>>> +Required properties:
>>>>> +  - compatible: Should be "maxim,max11100"
>>>>> +  - vref-supply: phandle to the regulator that provides reference voltage
>>>>> +
>>>>> +Optional properties:
>>>>> +  - spi-max-frequency: SPI maximum frequency
>>>>> +
>>>>> +Example:
>>>>> +
>>>>> +adc0: max11100@0 {
>>>>> +        compatible = "maxim,max11100";
>>>>> +        vref-supply = <&adc0_vref>;
>>>>> +        spi-max-frequency = <240000>;
>>>>> +};
>>>>> +
>>>>> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
>>>>> index 99c0514..a909484 100644
>>>>> --- a/drivers/iio/adc/Kconfig
>>>>> +++ b/drivers/iio/adc/Kconfig
>>>>> @@ -285,6 +285,15 @@ config MAX1027
>>>>>        To compile this driver as a module, choose M here: the module will be
>>>>>        called max1027.
>>>>>
>>>>> +config MAX11100
>>>>> +    tristate "Maxim max11100 ADC driver"
>>>>> +    depends on SPI
>>>>
>>>> SPI_MASTER is more precise I think
>>>>
>>>>> +    help
>>>>> +      Say yes here to build support for Maxim max11100 SPI ADC
>>>>> +
>>>>> +      To compile this driver as a module, choose M here: the module will be
>>>>> +      called max11100.
>>>>> +
>>>>>  config MAX1363
>>>>>      tristate "Maxim max1363 ADC driver"
>>>>>      depends on I2C
>>>>> diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
>>>>> index 7a40c04..1463044 100644
>>>>> --- a/drivers/iio/adc/Makefile
>>>>> +++ b/drivers/iio/adc/Makefile
>>>>> @@ -29,6 +29,7 @@ obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
>>>>>  obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o
>>>>>  obj-$(CONFIG_LTC2485) += ltc2485.o
>>>>>  obj-$(CONFIG_MAX1027) += max1027.o
>>>>> +obj-$(CONFIG_MAX11100) += max11100.o
>>>>>  obj-$(CONFIG_MAX1363) += max1363.o
>>>>>  obj-$(CONFIG_MCP320X) += mcp320x.o
>>>>>  obj-$(CONFIG_MCP3422) += mcp3422.o
>>>>> diff --git a/drivers/iio/adc/max11100.c b/drivers/iio/adc/max11100.c
>>>>> new file mode 100644
>>>>> index 0000000..f372ad8
>>>>> --- /dev/null
>>>>> +++ b/drivers/iio/adc/max11100.c
>>>>> @@ -0,0 +1,166 @@
>>>>> +/*
>>>>> + * iio/adc/max11100.c
>>>>> + * Maxim max11100 ADC Driver with IIO interface
>>>>> + *
>>>>> + * Copyright (C) 2016 Renesas Electronics Corporation
>>>>> + * Copyright (C) 2016 Jacopo Mondi
>>>>> + *
>>>>> + * 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.
>>>>> + */
>>>>> +#include <linux/delay.h>
>>>>> +#include <linux/kernel.h>
>>>>> +#include <linux/module.h>
>>>>> +#include <linux/regulator/consumer.h>
>>>>> +#include <linux/spi/spi.h>
>>>>> +
>>>>> +#include <linux/iio/iio.h>
>>>>> +#include <linux/iio/buffer.h>
>>>>> +#include <linux/iio/driver.h>
>>>>> +
>>>>> +/*
>>>>> + * LSB is the ADC single digital step
>>>>> + * 1 LSB = (vref / 2 ^ 16)
>>>>> + * AIN = (DIN * LSB)
>>>>> + */
>>>>> +#define MAX11100_LSB_DIV        (1 << 16)
>>>>> +#define MAX11100_LSB(vref)         (vref / MAX11100_LSB_DIV)
>>>>
>>>> maybe parenthesis around vref
>>>>
>>>>> +
>>>>> +struct max11100_state {
>>>>> +    const struct max11100_chip_desc *desc;
>>>>> +    struct spi_device *spi;
>>>>> +    int vref_uv;
>>>>> +    struct mutex lock;
>>>>> +};
>>>>> +
>>>>> +static struct iio_chan_spec max11100_channels[] = {
>>>>> +    { /* [0] */
>>>>> +        .type = IIO_VOLTAGE,
>>>>> +        .scan_type = {
>>>>
>>>> scan_type not needed since driver does not support buffered reads
>>>>
>>>>> +            .sign = 'u',
>>>>> +            .realbits = 16,
>>>>> +            .storagebits = 24,
>>>>> +            .shift = 8,
>>>>> +            .repeat = 1,
>>>>> +            .endianness = IIO_BE,
>>>>> +        },
>>>>> +        .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
>>>>> +    },
>>>>> +};
>>>>> +
>>>>> +static struct max11100_chip_desc {
>>>>> +    unsigned int num_chan;
>>>>> +    const struct iio_chan_spec *channels;
>>>>> +} max11100_desc = {
>>>>> +    .num_chan = ARRAY_SIZE(max11100_channels),
>>>>> +    .channels = max11100_channels,
>>>>> +};
>>>>> +
>>>>> +static int max11100_read_raw(struct iio_dev *indio_dev,
>>>>> +                 struct iio_chan_spec const *chan,
>>>>> +                 int *val, int *val2, long mask)
>>>>> +{
>>>>> +    int ret;
>>>>> +    struct max11100_state *state = iio_priv(indio_dev);
>>>>> +    uint8_t buffer[3];
>>>>> +
>>>>> +    mutex_lock(&state->lock);
>>>>> +
>>>>> +    ret = spi_read(state->spi, buffer, sizeof(buffer));
>>>>> +    if (ret) {
>>>>> +        mutex_unlock(&state->lock);
>>>>> +        dev_err(&indio_dev->dev, "SPI transfer failed\n");
>>>>> +        return ret;
>>>>> +    }
>>>>> +    mutex_unlock(&state->lock);
>>>>> +
>>>>> +    /* the first 8 bits sent out from ADC must be 0s */
>>>>> +    if (buffer[0]) {
>>>>> +        dev_err(&indio_dev->dev, "Invalid value: buffer[0] != 0\n");
>>>>> +        return -EINVAL;
>>>>> +    }
>>>>> +
>>>>> +    *val = be16_to_cpu(*(uint16_t *)&buffer[1]);
>>>>> +    *val = *val * MAX11100_LSB(state->vref_uv) / 1000;
>>>>
>>>> no, INFO_RAW shall not perform such scaling, use _PROCESSED or add an
>>>> INFO_SCALE to indicate the scaling
>>>
>>> Here I am not scaling the result, just converting the digital value read from ADC into millivolts.
>>> The transfer function from Din to Ain depends on vref, in the form reported in comments in file header:
>>>
>>> Ain = Din * (vref / 2^16)
>>>
>>> I am using microvolts as "vref" unit otherwise I would have been forced to deal with floating point arithmetic.
>> That's what the _scale elements of the IIO ABI meant for.  Make even this simple
>> conversion the job of userspace which is better placed to do any magic it wishes
>> to do with how it does the conversion (or whether it does depending on the
>> application).  So expectation is that raw means whatever came from the ADC so
>> ADC 'counts' not mV or similar.
>>
> 
> Ok, fine, I now get it.
> Userspace perform conversion using values returned from _RAW and _SCALE.
> 
> As the conversion process is device-specific (in my case is the
> simple transfer function reported some lines above), should it be
> documented somewhere?
It should conform to the documentation in 
Documentation/ABI/test/sysfs-bus-iio

Userspace needs to be sure that is the case, otherwise it'll never know what
to do with it.

Jonathan
> 
> Thanks j
> 
>> Jonathan
>>>
>>> Thanks
>>>    j
>>>
>>>>
>>>>> +
>>>>> +    return IIO_VAL_INT;
>>>>> +}
>>>>> +
>>>>> +static const struct iio_info max11100_info = {
>>>>> +    .driver_module = THIS_MODULE,
>>>>> +    .read_raw = max11100_read_raw,
>>>>> +};
>>>>> +
>>>>> +static int max11100_probe(struct spi_device *spi)
>>>>> +{
>>>>> +    int ret;
>>>>> +    struct iio_dev *indio_dev;
>>>>> +    struct regulator *vref_reg;
>>>>> +    struct max11100_state *state;
>>>>> +
>>>>> +    indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*state));
>>>>> +    if (!indio_dev)
>>>>> +        return -ENOMEM;
>>>>> +
>>>>> +    spi_set_drvdata(spi, indio_dev);
>>>>> +
>>>>> +    state = iio_priv(indio_dev);
>>>>> +    state->spi = spi;
>>>>> +    state->desc = &max11100_desc;
>>>>> +
>>>>> +    mutex_init(&state->lock);
>>>>> +
>>>>> +    indio_dev->dev.parent = &spi->dev;
>>>>> +    indio_dev->dev.of_node = spi->dev.of_node;
>>>>> +    indio_dev->info = &max11100_info;
>>>>> +    indio_dev->modes = INDIO_DIRECT_MODE;
>>>>> +    indio_dev->channels = state->desc->channels;
>>>>> +    indio_dev->num_channels = state->desc->num_chan;
>>>>> +
>>>>> +    vref_reg = devm_regulator_get(&spi->dev, "vref");
>>>>> +    if (IS_ERR(vref_reg))
>>>>> +        return PTR_ERR(vref_reg);
>>>>> +
>>>>> +    ret = regulator_enable(vref_reg);
>>>>> +    if (ret)
>>>>> +        return ret;
>>>>> +
>>>>> +    state->vref_uv = regulator_get_voltage(vref_reg);
>>>>> +    if (state->vref_uv < 0) {
>>>>> +        /* dummy regulator "get_voltage" returns -EINVAL as well */
>>>>> +        ret = -EINVAL;
>>>>> +        goto disable_regulator;
>>>>> +    }
>>>>> +
>>>>> +    ret = devm_iio_device_register(&spi->dev, indio_dev);
>>>>
>>>> the regulator needs to be disabled in a _remove() function and since you
>>>> need a remove function, devm_iio_device_register() should not be used
>>>>
>>>>> +    if (ret)
>>>>> +        goto disable_regulator;
>>>>> +
>>>>> +    return 0;
>>>>> +
>>>>> +disable_regulator:
>>>>> +    regulator_disable(vref_reg);
>>>>> +    return ret;
>>>>> +}
>>>>> +
>>>>> +static const struct of_device_id max11100_ids[] = {
>>>>> +    {.compatible = "maxim,max11100"},
>>>>> +    { },
>>>>> +};
>>>>> +MODULE_DEVICE_TABLE(of, max11100_ids);
>>>>> +
>>>>> +static struct spi_driver max11100_driver = {
>>>>> +    .driver = {
>>>>> +        .name    = "max11100",
>>>>> +        .owner    = THIS_MODULE,
>>>>> +        .of_match_table = of_match_ptr(max11100_ids),
>>>>> +    },
>>>>> +    .probe        = max11100_probe,
>>>>> +};
>>>>> +
>>>>> +module_spi_driver(max11100_driver);
>>>>> +
>>>>> +MODULE_AUTHOR("Jacopo Mondi <jacopo@jmondi.org>");
>>>>> +MODULE_DESCRIPTION("Maxim max11100 ADC Driver");
>>>>> +MODULE_LICENSE("GPL v2");
>>>>>
>>>>
>>>
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>>
>