Re: [PATCH 1/3] iio: amplifiers: hmc425a: Add support for HMC425A step attenuator with gpio interface

Jonathan Cameron
2020-01-18T13:54:47Z

On Mon, 13 Jan 2020 16:15:53 +0200
Beniamin Bia <beniamin.bia@analog.com> wrote:

> From: Michael Hennerich <michael.hennerich@analog.com>
>
> This patch adds support for the HMC425A 0.5 dB LSB GaAs MMIC 6-BIT
> DIGITAL POSITIVE CONTROL ATTENUATOR, 2.2 - 8.0 GHz.
>
> Datasheet:
> https://www.analog.com/media/en/technical-documentation/data-sheets/hmc425A.pdf
>
> Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>

I'll try and avoid replicate comments already made!

> ---
> drivers/iio/amplifiers/Kconfig | 10 ++
> drivers/iio/amplifiers/Makefile | 1 +
> drivers/iio/amplifiers/hmc425a.c | 247 +++++++++++++++++++++++++++++++
> 3 files changed, 258 insertions(+)
> create mode 100644 drivers/iio/amplifiers/hmc425a.c
>
> diff --git a/drivers/iio/amplifiers/Kconfig b/drivers/iio/amplifiers/Kconfig
> index da7f126d197b..9b02c9a2bc8a 100644
> --- a/drivers/iio/amplifiers/Kconfig
> +++ b/drivers/iio/amplifiers/Kconfig
> @@ -22,4 +22,14 @@ config AD8366
> To compile this driver as a module, choose M here: the
> module will be called ad8366.
>
> +config HMC425
> + tristate "Analog Devices HMC425A and similar GPIO Gain Amplifiers"
> + depends on GPIOLIB
> + help
> + Say yes here to build support for Analog Devices HMC425A and similar
> + gain amplifiers or step attenuators.
> +
> + To compile this driver as a module, choose M here: the
> + module will be called hmc425a.
> +
> endmenu
> diff --git a/drivers/iio/amplifiers/Makefile b/drivers/iio/amplifiers/Makefile
> index 9abef2ebe9bc..19a89db1d9b1 100644
> --- a/drivers/iio/amplifiers/Makefile
> +++ b/drivers/iio/amplifiers/Makefile
> @@ -5,3 +5,4 @@
>
> # When adding new entries keep the list in alphabetical order
> obj-$(CONFIG_AD8366) += ad8366.o
> +obj-$(CONFIG_HMC425) += hmc425a.o
> \ No newline at end of file
> diff --git a/drivers/iio/amplifiers/hmc425a.c b/drivers/iio/amplifiers/hmc425a.c
> new file mode 100644
> index 000000000000..525ebadaf1e8
> --- /dev/null
> +++ b/drivers/iio/amplifiers/hmc425a.c
> @@ -0,0 +1,247 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * HMC425A and similar Gain Amplifiers
> + *
> + * Copyright 2020 Analog Devices Inc.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of_device.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/regulator/consumer.h>
> +#include <linux/sysfs.h>
> +
> +enum hmc425a_type {
> + ID_HMC425A,
> +};
> +
> +struct hmc425a_chip_info {
> + const struct iio_chan_spec *channels;
> + unsigned int num_channels;
> + unsigned int num_gpios;
> + int gain_min;
> + int gain_max;
> + int default_gain;
> +};
> +
> +struct hmc425a_state {
> + struct regulator *reg;
> + struct mutex lock; /* protect sensor state */
> + struct hmc425a_chip_info *chip_info;
> + struct gpio_descs *gpios;
> + enum hmc425a_type type;
> + u32 gain;
> +};
> +
> +static int hmc425a_write(struct iio_dev *indio_dev, u32 value)
> +{
> + struct hmc425a_state *st = iio_priv(indio_dev);
> + int i, *values;
> +
> + values = kmalloc_array(st->chip_info->num_gpios, sizeof(int),
> + GFP_KERNEL);
> + if (!values)
> + return -ENOMEM;
> +
> + for (i = 0; i < st->chip_info->num_gpios; i++)
> + values[i] = (value >> i) & 1;
> +
> + gpiod_set_array_value_cansleep(st->gpios->ndescs, st->gpios->desc,
> + values);
> + kfree(values);
> + return 0;
> +}
> +
> +static int hmc425a_read_raw(struct iio_dev *indio_dev,
> + struct iio_chan_spec const *chan, int *val,
> + int *val2, long m)
> +{
> + struct hmc425a_state *st = iio_priv(indio_dev);
> + int code, gain = 0;
> + int ret;
> +
> + mutex_lock(&st->lock);
> + switch (m) {
> + case IIO_CHAN_INFO_HARDWAREGAIN:
> + code = st->gain;
> +
> + switch (st->type) {
> + case ID_HMC425A:
> + gain = ~code * -500;
> + break;
> + }
> +
> + /* Values in dB */
> + *val = gain / 1000;
> + *val2 = (gain % 1000) * 1000;
> +
> + ret = IIO_VAL_INT_PLUS_MICRO_DB;
> + break;
> + default:
> + ret = -EINVAL;
> + }
> + mutex_unlock(&st->lock);
> +
> + return ret;
> +};
> +
> +static int hmc425a_write_raw(struct iio_dev *indio_dev,
> + struct iio_chan_spec const *chan, int val,
> + int val2, long mask)
> +{
> + struct hmc425a_state *st = iio_priv(indio_dev);
> + struct hmc425a_chip_info *inf = st->chip_info;
> + int code = 0, gain;
> + int ret;
> +
> + /* Values in dB */

Are they?. For output values we have the IIO_VAL_INT_PLUS_MICRO_DB
formatting option, but I don't think we yet have any code in the
core to read in values in DB. I think all it would need to do is check
that dB occured after the number and provide a write_raw_get_fmt
callback to ensure the core knows to enforce this.

We may have an issue with other drivers around this though...
Possibly need some fuzzy logic to let them work but perhaps
print a warning once that they should postfix with dB.
What do people think?

> + if (val < 0)
> + gain = (val * 1000) - (val2 / 1000);
> + else
> + gain = (val * 1000) + (val2 / 1000);
> +
> + if (gain > inf->gain_max || gain < inf->gain_min)
> + return -EINVAL;
> +
> + switch (st->type) {
> + case ID_HMC425A:
> + code = ~((abs(gain) / 500) & 0x3F);
> + break;
> + }
> +
> + mutex_lock(&st->lock);
> + switch (mask) {
> + case IIO_CHAN_INFO_HARDWAREGAIN:
> + st->gain = code;
> +
> + ret = hmc425a_write(indio_dev, st->gain);
> + break;
> + default:
> + ret = -EINVAL;
> + }
> + mutex_unlock(&st->lock);
> +
> + return ret;
> +}
> +
> +static const struct iio_info hmc425a_info = {
> + .read_raw = &hmc425a_read_raw,
> + .write_raw = &hmc425a_write_raw,
> +};
> +
> +#define HMC425A_CHAN(_channel) \
> +{ \
> + .type = IIO_VOLTAGE, .output = 1, .indexed = 1, \
> + .channel = _channel, \
> + .info_mask_separate = BIT(IIO_CHAN_INFO_HARDWAREGAIN), \
> +}
> +
> +static const struct iio_chan_spec hmc425a_channels[] = {
> + HMC425A_CHAN(0),
> +};
> +
> +/* Match table for of_platform binding */
> +static const struct of_device_id hmc425a_of_match[] = {
> + { .compatible = "adi,hmc425a", .data = (void *)ID_HMC425A },
> + {},
> +};
> +MODULE_DEVICE_TABLE(of, hmc425a_of_match);
> +
> +static void hmc425a_remove(void *data)
> +{
> + struct hmc425a_state *st = data;
> +
> + regulator_disable(st->reg);
> +}
> +
> +static struct hmc425a_chip_info hmc425a_chip_info_tbl[] = {
> + [ID_HMC425A] = {
> + .channels = hmc425a_channels,
> + .num_channels = ARRAY_SIZE(hmc425a_channels),
> + .num_gpios = 6,
> + .gain_min = -31500,
> + .gain_max = 0,
> + .default_gain = -0x40, /* set default gain -31.5db*/
> + },
> +};
> +
> +static int hmc425a_probe(struct platform_device *pdev)
> +{
> + struct device_node *np = pdev->dev.of_node;
> + const struct of_device_id *id;
> + struct iio_dev *indio_dev;
> + struct hmc425a_state *st;
> + int ret;
> +
> + indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(*st));
> + if (!indio_dev)
> + return -ENOMEM;
> +
> + st = iio_priv(indio_dev);
> + id = of_match_device(hmc425a_of_match, &pdev->dev);
> + if (!id)
> + ret = -ENODEV;
> +
> + st->type = (enum hmc425a_type)id->data;
> +
> + st->chip_info = &hmc425a_chip_info_tbl[st->type];
> + indio_dev->num_channels = st->chip_info->num_channels;
> + indio_dev->channels = st->chip_info->channels;
> + st->gain = st->chip_info->default_gain;
> +
> + st->gpios = devm_gpiod_get_array(&pdev->dev, "ctrl", GPIOD_OUT_LOW);
> + if (IS_ERR(st->gpios)) {
> + ret = PTR_ERR(st->gpios);
> + if (ret != -EPROBE_DEFER)
> + dev_err(&pdev->dev, "failed to get gpios\n");
> + return ret;
> + }
> +
> + if (st->gpios->ndescs != st->chip_info->num_gpios) {
> + dev_err(&pdev->dev, "%d GPIOs needed to operate\n",
> + st->chip_info->num_gpios);
> + return -ENODEV;
> + }
> +
> + st->reg = devm_regulator_get(&pdev->dev, "vcc");

> + if (!IS_ERR(st->reg)) {

Ideally handle deferred probing. We might have a retlator
specified but not have it yet.

Don't paper over not finding it. options are:
1) regulator framework not built. Stubs won't return errors so fine.
2) regulator info not supplied. A fake 'stub' regulator will be
return which will work fine (just not do anything). This is often
desirable when the power line isn't controllable.
3) actual regulator but driver not loaded yet. For those we need to
ensure we return with -EDEFER. That will be returned by devm_regulator_get
if that happens.
4) regulator there and it all works perfectly.

For none of the above is skipping over this section the right thing to do.

> + ret = regulator_enable(st->reg);
> + if (ret)
> + return ret;
> + ret = devm_add_action_or_reset(&pdev->dev, hmc425a_remove, st);

Given this just disables the regulator rather than being a conventional
driver remove, give it a different name.

> + if (ret)
> + return ret;
> + }
> +
> + platform_set_drvdata(pdev, indio_dev);
> + mutex_init(&st->lock);
> +
> + indio_dev->dev.parent = &pdev->dev;
> + indio_dev->name = np->name;
> + indio_dev->info = &hmc425a_info;
> + indio_dev->modes = INDIO_DIRECT_MODE;
> +
> + return devm_iio_device_register(&pdev->dev, indio_dev);
> +}
> +
> +static struct platform_driver hmc425a_driver = {
> + .driver = {
> + .name = KBUILD_MODNAME,
> + .of_match_table = hmc425a_of_match,
> + },
> + .probe = hmc425a_probe,
> +};
> +module_platform_driver(hmc425a_driver);
> +
> +MODULE_AUTHOR("Michael Hennerich <michael.hennerich@analog.com>");
> +MODULE_DESCRIPTION(
> + "Analog Devices HMC425A and similar GPIO control Gain Amplifiers");

Just leave that on one line and don't worry about 80 chars limit.
Its more 'advise' than a hard rule ;)

> +MODULE_LICENSE("GPL v2");