RE: [PATCH 1/3] iio:amplifiers:ada4250: add support for ADA4250

From: Miclaus, Antoniu
Date: Fri Feb 11 2022 - 08:41:31 EST

> -----Original Message-----
> From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> Sent: Friday, February 11, 2022 2:46 PM
> To: Miclaus, Antoniu <Antoniu.Miclaus@xxxxxxxxxx>
> Cc: jic23@xxxxxxxxxx; robh+dt@xxxxxxxxxx; linux-iio@xxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH 1/3] iio:amplifiers:ada4250: add support for ADA4250
>
> [External]
>
> On Fri, 11 Feb 2022 11:50:55 +0200
> Antoniu Miclaus <antoniu.miclaus@xxxxxxxxxx> wrote:
>
> > The ADA4250 is an instrumentation amplifier with SPI/pin-strap
> > progammable gains that is optimized for ultra-low power systems.
> > With a minimum supply voltage of 1.7V, 26uA of quiescent current,
> > a shutdown mode, a sleep mode, and a fast wake up settling time,
> > ADA4250 can be power cycled on a battery powered system for even
> > futher savings.
> >
> > Signed-off-by: Antoniu Miclaus <antoniu.miclaus@xxxxxxxxxx>
>
> Hi Antoniu,
>
> Just to check, this sort of amplifier is normally not used as
> an analog front end? If it were we'd want to deal with it
> being a consumer of the ADC channels similar to our other AFE drivers.
> If that's a possible usecase we might want to consider how to support
> that if relevant to a particular configuration.
>
> I don't understand what the two channels are. Could you give us
> some more description?
>
> Thanks,
>
> Jonathan

Hello Jonathan,

This is a basic amplifier part, that receives a voltage as input and applies a gain/offset to it.

I initially added a single IIO voltage channel having all the below attributes.
But the gain has no measurement unit (V/V), as specified in `hwgain_table[]` comment.
Same for the current bias setting (see `calibbias_table` comment).

Also I wanted to somehow emphasize that the scaling applies only to the offset value
which is passed in uV so we can avoid floating point computations.
The output offset raw value is computed based on the input voltage value set by the user.
Depending on that value, and the current bias setting, a table of values/equations is provided
in the documentation that establishes the VLSB/range values that need to be written in the
afferent registers (the entire computation is done in the `set_offset` function).

Regards,
Antoniu
>
> > ---
> > drivers/iio/amplifiers/Kconfig | 11 +
> > drivers/iio/amplifiers/Makefile | 1 +
> > drivers/iio/amplifiers/ada4250.c | 388
> +++++++++++++++++++++++++++++++
> > 3 files changed, 400 insertions(+)
> > create mode 100644 drivers/iio/amplifiers/ada4250.c
> >
> > diff --git a/drivers/iio/amplifiers/Kconfig b/drivers/iio/amplifiers/Kconfig
> > index 5eb1357a9c78..98612e01d9d4 100644
> > --- a/drivers/iio/amplifiers/Kconfig
> > +++ b/drivers/iio/amplifiers/Kconfig
> > @@ -23,6 +23,17 @@ config AD8366
> > To compile this driver as a module, choose M here: the
> > module will be called ad8366.
> >
> > +config ADA4250
> > + tristate "Analog Devices ADA4250 Instrumentation Amplifier"
> > + depends on SPI
> > + help
> > + Say yes here to build support for Analog Devices ADA4250
> > + SPI Amplifier's support. The driver provides direct access via
> > + sysfs.
>
> Odd spacing.
>
> > +
> > + To compile this driver as a module, choose M here: the
> > + module will be called ada4250.
> > +
> > config HMC425
> > tristate "Analog Devices HMC425A and similar GPIO Gain Amplifiers"
> > depends on GPIOLIB
> > diff --git a/drivers/iio/amplifiers/Makefile b/drivers/iio/amplifiers/Makefile
> > index cb551d82f56b..2126331129cf 100644
> > --- a/drivers/iio/amplifiers/Makefile
> > +++ b/drivers/iio/amplifiers/Makefile
> > @@ -5,4 +5,5 @@
> >
> > # When adding new entries keep the list in alphabetical order
> > obj-$(CONFIG_AD8366) += ad8366.o
> > +obj-$(CONFIG_ADA4250) += ada4250.o
> > obj-$(CONFIG_HMC425) += hmc425a.o
> > diff --git a/drivers/iio/amplifiers/ada4250.c
> b/drivers/iio/amplifiers/ada4250.c
> > new file mode 100644
> > index 000000000000..10725f6c2751
> > --- /dev/null
> > +++ b/drivers/iio/amplifiers/ada4250.c
> > @@ -0,0 +1,388 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * ADA4250 driver
> > + *
> > + * Copyright 2022 Analog Devices Inc.
> > + */
> > +
> > +#include <linux/bitfield.h>
> > +#include <linux/bits.h>
> > +#include <linux/device.h>
> > +#include <linux/iio/iio.h>
> > +#include <linux/module.h>
> > +#include <linux/regmap.h>
> > +#include <linux/regulator/consumer.h>
> > +#include <linux/spi/spi.h>
> > +
> > +/* ADA4250 Register Map */
> > +#define ADA4250_REG_GAIN_MUX 0x00
> > +#define ADA4250_REG_REFBUF_EN 0x01
> > +#define ADA4250_REG_RESET 0x02
> > +#define ADA4250_REG_SNSR_CAL_VAL 0x04
> > +#define ADA4250_REG_SNSR_CAL_CNFG 0x05
> > +#define ADA4250_REG_DIE_REV 0x18
> > +#define ADA4250_REG_CHIP_ID 0x19
> > +
> > +/* ADA4250_REG_GAIN_MUX Map */
> > +#define ADA4250_GAIN_MUX_MSK GENMASK(2, 0)
> > +
> > +/* ADA4250_REG_REFBUF Map */
> > +#define ADA4250_REFBUF_MSK BIT(0)
> > +
> > +/* ADA4250_REG_RESET Map */
> > +#define ADA4250_RESET_MSK BIT(0)
> > +
> > +/* ADA4250_REG_SNSR_CAL_VAL Map */
> > +#define ADA4250_SNSR_CAL_VAL_MSK GENMASK(7, 0)
> > +
> > +/* ADA4250_REG_SNSR_CAL_CNFG Bit Definition */
> > +#define ADA4250_BIAS_SET_MSK GENMASK(3, 2)
> > +#define ADA4250_RANGE_SET_MSK GENMASK(1, 0)
> > +
> > +/* Miscellaneous definitions */
> > +#define ADA4250_CHIP_ID 0x4250
> > +#define ADA4250_RANGE1 0
> > +#define ADA4250_RANGE4 3
> > +
> > +/* ADA4250 current bias set */
> > +enum ada4250_current_bias {
> > + ADA4250_BIAS_DISABLED,
> > + ADA4250_BIAS_BANDGAP,
> > + ADA4250_BIAS_AVDD,
> > +};
> > +
> > +struct ada4250_state {
> > + struct spi_device *spi;
> > + struct regmap *regmap;
> > + struct regulator *reg;
> > + /* Protect against concurrent accesses to the device and data
> content */
> > + struct mutex lock;
> > + u8 bias;
> > + u8 gain;
> > + int offset_uv;
> > + bool refbuf_en;
> > +};
> > +
> > +/* ADA4250 Current Bias Source Settings: Disabled, Bandgap Reference,
> AVDD */
> > +static const int calibbias_table[] = {0, 1, 2};
> > +
> > +/* ADA4250 Gain (V/V) values: 1, 2, 4, 8, 16, 32, 64, 128 */
> > +static const int hwgain_table[] = {0, 1, 2, 3, 4, 5, 6, 7};
> > +
> > +static const struct regmap_config ada4250_regmap_config = {
> > + .reg_bits = 8,
> > + .val_bits = 8,
> > + .read_flag_mask = BIT(7),
> > + .max_register = 0x1A,
> > +};
> > +
> > +static int ada4250_set_offset_uv(struct iio_dev *indio_dev,
> > + const struct iio_chan_spec *chan,
> > + int offset_uv)
> > +{
> > + struct ada4250_state *st = iio_priv(indio_dev);
> > +
> > + int i, ret, x[8], max_vos, min_vos, voltage_v, vlsb = 0;
> > + u8 offset_raw, range = ADA4250_RANGE1;
> > + u32 lsb_coeff[6] = {1333, 2301, 4283, 8289, 16311, 31599};
> > +
> > + if (st->bias == 0 || st->bias == 3)
> > + return -EINVAL;
> > +
> > + voltage_v = regulator_get_voltage(st->reg);
> > + voltage_v = DIV_ROUND_CLOSEST(voltage_v, 1000000);
> > +
> > + if (st->bias == ADA4250_BIAS_AVDD)
> > + x[0] = voltage_v;
> > + else
> > + x[0] = 5;
> > +
> > + x[1] = 126 * (x[0] - 1);
> > +
> > + for (i = 0; i < 6; i++)
> > + x[i + 2] = DIV_ROUND_CLOSEST(x[1] * 1000, lsb_coeff[i]);
> > +
> > + if (st->gain == 0)
> > + return -EINVAL;
> > +
> > + /* Compute Range and VLSB for the Sensor Offset Calibration */
> > + for (i = ADA4250_RANGE1; i <= ADA4250_RANGE4; i++) {
> > + max_vos = x[st->gain] * 127 * ((1 << (i + 1)) - 1);
> > + min_vos = -1 * max_vos;
> > + if (offset_uv > min_vos && offset_uv < max_vos) {
> > + range = i;
> > + vlsb = x[st->gain] * ((1 << (i + 1)) - 1);
> > + break;
> > + }
> > + }
> > +
> > + if (vlsb <= 0)
> > + return -EINVAL;
> > +
> > + offset_raw = DIV_ROUND_CLOSEST(abs(offset_uv), vlsb);
> > +
> > + mutex_lock(&st->lock);
> > + ret = regmap_update_bits(st->regmap,
> ADA4250_REG_SNSR_CAL_CNFG,
> > + ADA4250_RANGE_SET_MSK,
> > + FIELD_PREP(ADA4250_RANGE_SET_MSK,
> range));
> > + if (ret)
> > + goto exit;
> > +
> > + st->offset_uv = offset_raw * vlsb;
> > +
> > + if (offset_uv < 0) {
> > + offset_raw |= 1 << 8;
> > + st->offset_uv *= (-1);
> > + }
> > +
> > + ret = regmap_write(st->regmap, ADA4250_REG_SNSR_CAL_VAL,
> offset_raw);
> > +
> > +exit:
> > + mutex_unlock(&st->lock);
> > +
> > + return ret;
> > +}
> > +
> > +static int ada4250_read_raw(struct iio_dev *indio_dev,
> > + struct iio_chan_spec const *chan,
> > + int *val, int *val2, long info)
> > +{
> > + struct ada4250_state *st = iio_priv(indio_dev);
> > + int ret;
> > +
> > + switch (info) {
> > + case IIO_CHAN_INFO_HARDWAREGAIN:
> > + ret = regmap_read(st->regmap, ADA4250_REG_GAIN_MUX,
> val);
> > + if (ret)
> > + return ret;
> > +
> > + return IIO_VAL_INT;
> > + case IIO_CHAN_INFO_OFFSET:
> > + *val = st->offset_uv;
> > +
> > + return IIO_VAL_INT;
> > + case IIO_CHAN_INFO_CALIBBIAS:
> > + ret = regmap_read(st->regmap,
> ADA4250_REG_SNSR_CAL_CNFG, val);
> > + if (ret)
> > + return ret;
> > +
> > + *val = FIELD_GET(ADA4250_BIAS_SET_MSK, *val);
> > +
> > + return IIO_VAL_INT;
> > + case IIO_CHAN_INFO_SCALE:
> > + *val = 1;
> > + *val2 = 1000000;
> > +
> > + return IIO_VAL_FRACTIONAL;
> > + default:
> > + return -EINVAL;
> > + }
> > +}
> > +
> > +static int ada4250_write_raw(struct iio_dev *indio_dev,
> > + struct iio_chan_spec const *chan,
> > + int val, int val2, long info)
> > +{
> > + struct ada4250_state *st = iio_priv(indio_dev);
> > + int ret;
> > +
> > + switch (info) {
> > + case IIO_CHAN_INFO_HARDWAREGAIN:
> > + ret = regmap_write(st->regmap, ADA4250_REG_GAIN_MUX,
> > + FIELD_PREP(ADA4250_GAIN_MUX_MSK,
> val));
> > + if (ret)
> > + return ret;
> > +
> > + st->gain = val;
> > +
> > + return ret;
> > + case IIO_CHAN_INFO_OFFSET:
>
> Given no DS, please provide some more info on what the channels are to
> help evaluate if this is the appropriate interface.
>
> > + return ada4250_set_offset_uv(indio_dev, chan, val);
> > + case IIO_CHAN_INFO_CALIBBIAS:
> > + ret = regmap_update_bits(st->regmap,
> ADA4250_REG_SNSR_CAL_CNFG,
> > + ADA4250_BIAS_SET_MSK,
> > +
> FIELD_PREP(ADA4250_BIAS_SET_MSK, val));
> > + if (ret)
> > + return ret;
> > +
> > + st->bias = val;
> > +
> > + return ret;
> > + default:
> > + return -EINVAL;
> > + }
> > +}
> > +
> > +static int ada4250_read_avail(struct iio_dev *indio_dev,
> > + struct iio_chan_spec const *chan,
> > + const int **vals, int *type, int *length,
> > + long mask)
> > +{
> > + switch (mask) {
> > + case IIO_CHAN_INFO_CALIBBIAS:
> > + *vals = calibbias_table;
> > + *type = IIO_VAL_INT;
> > + *length = ARRAY_SIZE(calibbias_table);
> > +
> > + return IIO_AVAIL_LIST;
> > + case IIO_CHAN_INFO_HARDWAREGAIN:
> > + *vals = hwgain_table;
> > + *type = IIO_VAL_INT;
> > + *length = ARRAY_SIZE(hwgain_table);
> > +
> > + return IIO_AVAIL_LIST;
> > + default:
> > + return -EINVAL;
> > + }
> > +}
> > +
> > +static int ada4250_reg_access(struct iio_dev *indio_dev,
> > + unsigned int reg,
> > + unsigned int write_val,
> > + unsigned int *read_val)
> > +{
> > + struct ada4250_state *st = iio_priv(indio_dev);
> > +
> > + if (read_val)
> > + return regmap_read(st->regmap, reg, read_val);
> > + else
> > + return regmap_write(st->regmap, reg, write_val);
> > +}
> > +
> > +static const struct iio_info ada4250_info = {
> > + .read_raw = ada4250_read_raw,
> > + .write_raw = ada4250_write_raw,
> > + .read_avail = &ada4250_read_avail,
> > + .debugfs_reg_access = &ada4250_reg_access,
> > +};
> > +
> > +static const struct iio_chan_spec ada4250_channels[] = {
> > + {
> > + .type = IIO_ALTVOLTAGE,
>
> For a device like this, I'd argue it's not 'necessarily' an alternating
> voltage so type should probably be just voltage. Obviously if there
> is something about the amplifier architecture that means it won't carry
> DC then it's a different matter.
>
> > + .output = 1,
> > + .indexed = 1,
> > + .channel = 0,
> > + .info_mask_separate = BIT(IIO_CHAN_INFO_CALIBBIAS) |
> > + BIT(IIO_CHAN_INFO_HARDWAREGAIN),
> > + .info_mask_separate_available =
> BIT(IIO_CHAN_INFO_CALIBBIAS) |
> > +
> BIT(IIO_CHAN_INFO_HARDWAREGAIN),
> > + },
> > + {
> > + .type = IIO_VOLTAGE,
>
> Given we have no datasheet, what's this? Add a comment.
>
> > + .output = 1,
> > + .indexed = 1,
> > + .channel = 0,
> > + .info_mask_separate = BIT(IIO_CHAN_INFO_OFFSET) |
> > + BIT(IIO_CHAN_INFO_SCALE),
>
> This is unusual as I'm not sure what meaning an offset and scale have
> with out a raw value.
>
> > + },
> > +};
> > +
> > +static void ada4250_reg_disable(void *data)
> > +{
> > + regulator_disable(data);
> > +}
> > +
> > +static int ada4250_init(struct ada4250_state *st)
> > +{
> > + int ret;
> > + u16 chip_id;
> > + u8 data[2];
> > + struct spi_device *spi = st->spi;
> > +
> > + st->refbuf_en = device_property_read_bool(&spi->dev, "adi,refbuf-
> enable");
> > +
> > + st->reg = devm_regulator_get(&spi->dev, "avdd");
> > + if (IS_ERR(st->reg))
> > + return dev_err_probe(&spi->dev, PTR_ERR(st->reg),
> > + "failed to get the AVDD voltage\n");
> > +
> > + ret = regulator_enable(st->reg);
> > + if (ret) {
> > + dev_err(&spi->dev, "Failed to enable specified AVDD
> supply\n");
> > + return ret;
> > + }
> > +
> > + ret = devm_add_action_or_reset(&spi->dev, ada4250_reg_disable,
> st->reg);
> > + if (ret)
> > + return ret;
> > +
> > + ret = regmap_write(st->regmap, ADA4250_REG_RESET,
> > + FIELD_PREP(ADA4250_RESET_MSK, 1));
> > + if (ret)
> > + return ret;
> > +
> > + ret = regmap_bulk_read(st->regmap, ADA4250_REG_CHIP_ID, data,
> 2);
> I think our current position is that regmap_bulk_* accesses should use
> DMA safe buffers (on SPI anyway) as it's possible the implementation may
> required that and it isn't documented as not requiring it.
>
> > + if (ret)
> > + return ret;
> > +
> > + chip_id = (data[1] << 8) | data[0];
>
> Endian conversion. Firstly make data the appropriate type then use
> the appropriate endian conversion function.
>
> > +
> > + if (chip_id != ADA4250_CHIP_ID) {
> > + dev_err(&spi->dev, "Invalid chip ID.\n");
> > + return -EINVAL;
> > + }
> > +
> > + return regmap_write(st->regmap, ADA4250_REG_REFBUF_EN,
> > + FIELD_PREP(ADA4250_REFBUF_MSK, st-
> >refbuf_en));
> > +}
> > +
>