Re: [PATCH 3/3] iio: amplifiers: hmc425a: add support for LTC6373 Instrumentation Amplifier

[Jonathan Cameron]

On Thu, 21 Dec 2023 13:38:40 +0200
Dumitru Ceclan <mitrutzceclan@xxxxxxxxx> 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@xxxxxxxxx>
One trivial comment inline.

The use of IIO_INFO_ENABLE is unusual. So far the only documented uses of
that are

What:		/sys/.../iio:deviceX/in_energy_en
What:		/sys/.../iio:deviceX/in_distance_en
What:		/sys/.../iio:deviceX/in_velocity_sqrt(x^2+y^2+z^2)_en
What:		/sys/.../iio:deviceX/in_steps_en
KernelVersion:	3.19
Contact:	linux-iio@xxxxxxxxxxxxxxx
Description:
		Activates a device feature that runs in firmware/hardware.
		E.g. for steps: the pedometer saves power while not used;
		when activated, it will count the steps taken by the user in
		firmware and export them through in_steps_input.

And this doesn't match up with these sort of 'counting' or 'cumulative' measures.

I wonder treating it like a DAC output and instead using _powerdown
instead?

 ---
>  drivers/iio/amplifiers/hmc425a.c | 78 +++++++++++++++++++++++++++++++-
>  1 file changed, 76 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/amplifiers/hmc425a.c b/drivers/iio/amplifiers/hmc425a.c
> index b5fd19403d15..27fdc32a0457 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 +21,23 @@
>  #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_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 {
> @@ -42,6 +56,8 @@ struct hmc425a_state {
>  	struct	gpio_descs *gpios;
>  	enum	hmc425a_type type;
>  	u32	gain;
> +	bool	enabled;
> +
>  };
>  
>  static int hmc425a_write(struct iio_dev *indio_dev, u32 value)
> @@ -80,6 +96,17 @@ 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;
>  		break;
> +	case ID_LTC6373:
> +		if (!st->enabled)
> +			return -EPERM;
> +
> +		/* add half of the value for rounding */
> +		temp = LTC6373_CONVERSION_CONSTANT / 2;
> +		if (val < 0)
> +			temp *= -1;
> +		*code = ~((gain + temp) / LTC6373_CONVERSION_CONSTANT + 3)
> +			& LTC6373_CONVERSION_MASK;
> +		break;
>  	}
>  	return 0;
>  }
> @@ -100,6 +127,12 @@ 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->enabled)
> +			return -EPERM;
> +		gain = ((~code & LTC6373_CONVERSION_MASK) - 3) *
> +		       LTC6373_CONVERSION_CONSTANT;
> +		break;
>  	}
>  
>  	*val = gain / 1000;
> @@ -122,6 +155,10 @@ static int hmc425a_read_raw(struct iio_dev *indio_dev,
>  			break;
>  		ret = IIO_VAL_INT_PLUS_MICRO_DB;
>  		break;
> +	case IIO_CHAN_INFO_ENABLE:
> +		*val = st->enabled;
> +		ret = IIO_VAL_INT;
> +		break;
>  	default:
>  		ret = -EINVAL;
>  	}
> @@ -146,6 +183,17 @@ static int hmc425a_write_raw(struct iio_dev *indio_dev,
>  		st->gain = code;
>  		ret = hmc425a_write(indio_dev, st->gain);
>  		break;
> +	case IIO_CHAN_INFO_ENABLE:
> +		switch (st->type) {
> +		case ID_LTC6373:
> +			code = (val) ? st->gain : LTC6373_SHUTDOWN;
> +			st->enabled = val;
> +			ret = hmc425a_write(indio_dev, code);
> +			break;
> +		default:
> +			ret = -EINVAL;
> +		}
> +		break;
>  	default:
>  		ret = -EINVAL;
>  	}
> @@ -161,6 +209,8 @@ static int hmc425a_write_raw_get_fmt(struct iio_dev *indio_dev,
>  	switch (mask) {
>  	case IIO_CHAN_INFO_HARDWAREGAIN:
>  		return IIO_VAL_INT_PLUS_MICRO_DB;
> +	case IIO_CHAN_INFO_ENABLE:
> +		return IIO_VAL_INT;
>  	default:
>  		return -EINVAL;
>  	}
> @@ -181,15 +231,30 @@ static const struct iio_info hmc425a_info = {
>  	.info_mask_separate = BIT(IIO_CHAN_INFO_HARDWAREGAIN),		\
>  }
>  
> +#define LTC6373_CHAN(_channel)						\
> +{									\
> +	.type = IIO_VOLTAGE,						\
> +	.output = 1,							\
> +	.indexed = 1,							\
> +	.channel = _channel,						\
> +	.info_mask_separate = BIT(IIO_CHAN_INFO_HARDWAREGAIN) |		\
> +			      BIT(IIO_CHAN_INFO_ENABLE),		\
> +}
> +
>  static const struct iio_chan_spec hmc425a_channels[] = {
>  	HMC425A_CHAN(0),
>  };
>  
> +static const struct iio_chan_spec ltc6373_channels[] = {
> +	LTC6373_CHAN(0),
> +};
> +
>  /* Match table for of_platform binding */
>  static const struct of_device_id hmc425a_of_match[] = {
>  	{ .compatible = "adi,hmc425a", .data = (void *)ID_HMC425A },
>  	{ .compatible = "adi,hmc540s", .data = (void *)ID_HMC540S },
>  	{ .compatible = "adi,adrf5740", .data = (void *)ID_ADRF5740 },
> +	{ .compatible = "adi,ltc6373", .data = (void *)ID_LTC6373 },
>  	{},
>  };
>  MODULE_DEVICE_TABLE(of, hmc425a_of_match);
> @@ -222,6 +287,15 @@ static struct hmc425a_chip_info hmc425a_chip_info_tbl[] = {
>  		.gain_max = 0,
>  		.default_gain = 0xF, /* set default gain -22.0db*/
>  	},
> +		[ID_LTC6373] = {

Looks to be one tab too far indented.

> +		.name = "ltc6373",
> +		.channels = ltc6373_channels,
> +		.num_channels = ARRAY_SIZE(ltc6373_channels),
> +		.num_gpios = 3,
> +		.gain_min = -12041, /* gain setting x0.25*/
> +		.gain_max = 24082,  /* gain setting x16  */
> +		.default_gain = LTC6373_SHUTDOWN,
> +	},
>  };
>  
>  static int hmc425a_probe(struct platform_device *pdev)