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

[Jonathan Cameron <jic23@kernel.org>]

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.


> +};