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

[Dumitru Ceclan]

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>
---
 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] = {
+		.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)
-- 
2.42.0