Re: [PATCH v4 5/5] iio: amplifiers: hmc425a: add support for LTC6373 Instrumentation Amplifier

Jonathan Cameron
2024-01-21T17:14:34Z

On Wed, 17 Jan 2024 14:51:14 +0200
Dumitru Ceclan <mitrutzceclan@gmail.com> wrote:

> This adds support for LTC6373 36 V Fully-Differential Programmable-Gain
> Instrumentation Amplifier with 25 pA Input Bias Current.
> The user can program the gain to one of seven available settings through
> a 3-bit parallel interface (A2 to A0).
>
> Signed-off-by: Dumitru Ceclan <mitrutzceclan@gmail.com>
Hi Dumitru,

Some comments inline. I'd forgotten we have a rich set of DIV_xxx macros
in math.h, DIV_ROUND_CLOSEST is I think the same as what you have
coded up in here.

> ---
> drivers/iio/amplifiers/hmc425a.c | 118 +++++++++++++++++++++++++++++--
> 1 file changed, 114 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/iio/amplifiers/hmc425a.c b/drivers/iio/amplifiers/hmc425a.c
> index b116b54e4206..e7f425677fd3 100644
> --- a/drivers/iio/amplifiers/hmc425a.c
> +++ b/drivers/iio/amplifiers/hmc425a.c
> @@ -2,9 +2,10 @@
> /*
> * HMC425A and similar Gain Amplifiers
> *
> - * Copyright 2020 Analog Devices Inc.
> + * Copyright 2020, 2023 Analog Devices Inc.
> */
>
> +#include <linux/bits.h>
> #include <linux/bitops.h>
> #include <linux/device.h>
> #include <linux/err.h>
> @@ -20,10 +21,24 @@
> #include <linux/regulator/consumer.h>
> #include <linux/sysfs.h>
>
> +/*
> + * The LTC6373 amplifier supports configuring gain using GPIO's with the following
> + * values (OUTPUT_V / INPUT_V): 0(shutdown), 0.25, 0.5, 1, 2, 4, 8, 16
> + *
> + * Except for the shutdown value, all can be converted to dB using 20 * log10(x)
> + * From here, it is observed that all values are multiples of the '2' gain setting,
> + * with the correspondent of 6.020dB.
> + */
> +#define LTC6373_CONVERSION_CONSTANT 6020
> +#define LTC6373_MIN_GAIN_CODE 0x6
> +#define LTC6373_CONVERSION_MASK GENMASK(2, 0)
> +#define LTC6373_SHUTDOWN GENMASK(2, 0)
> +
> enum hmc425a_type {
> ID_HMC425A,
> ID_HMC540S,
> - ID_ADRF5740
> + ID_ADRF5740,
> + ID_LTC6373,
> };
>
> struct hmc425a_chip_info {
> @@ -34,6 +49,8 @@ struct hmc425a_chip_info {
> int gain_min;
> int gain_max;
> int default_gain;
> + int powerdown_val;
> + bool has_powerdown;
> };
>
> struct hmc425a_state {
> @@ -42,6 +59,7 @@ struct hmc425a_state {
> struct gpio_descs *gpios;
> enum hmc425a_type type;
> u32 gain;
> + bool powerdown;
> };
>
> static int hmc425a_write(struct iio_dev *indio_dev, u32 value)
> @@ -80,6 +98,17 @@ static int hmc425a_gain_dB_to_code(struct hmc425a_state *st, int val, int val2,
> temp = (abs(gain) / 2000) & 0xF;
> *code = temp & BIT(3) ? temp | BIT(2) : temp;
> return 0;
> + case ID_LTC6373:
> + if (st->powerdown)
> + return -EPERM;
> +
> + /* add half of the value for rounding */
> + temp = LTC6373_CONVERSION_CONSTANT / 2;

As mentioned in review of earlier patch, I'd like this to be in a callback not
based on st->type (which should be removed from the driver).

> + if (val < 0)
> + temp *= -1;
> + *code = ~((gain + temp) / LTC6373_CONVERSION_CONSTANT + 3)

I'd forgotten in previous reviews that we have DIV_ROUND_CLOSEST() that does
pretty similar maths to your handling here. Better to use that than
spin your own version.

> + & LTC6373_CONVERSION_MASK;
> + return 0;
> default:
> return -EINVAL;
> }
> @@ -101,6 +130,12 @@ static int hmc425a_code_to_gain_dB(struct hmc425a_state *st, int *val, int *val2
> code = code & BIT(3) ? code & ~BIT(2) : code;
> gain = code * -2000;
> break;
> + case ID_LTC6373:
> + if (st->powerdown)
> + return -EPERM;
> + gain = ((~code & LTC6373_CONVERSION_MASK) - 3) *
> + LTC6373_CONVERSION_CONSTANT;
> + break;
> }
>
> *val = gain / 1000;
> @@ -174,6 +209,48 @@ static const struct iio_info hmc425a_info = {
> .write_raw_get_fmt = &hmc425a_write_raw_get_fmt,
> };
>

> +
> +static const struct iio_chan_spec_ext_info ltc6373_ext_info[] = {
> + {
> + .name = "powerdown",
> + .read = ltc6373_read_powerdown,
> + .write = ltc6373_write_powerdown,
> + .shared = IIO_SEPARATE,
> + },
> + {},

No comma preferred after a terminator entry like this as nothing should
ever come after it. Any new additions must be before this last entry.

> +};