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

Dumitru Ceclan
2024-01-17T12:51:40Z

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>
---
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;
+ if (val < 0)
+ temp *= -1;
+ *code = ~((gain + temp) / LTC6373_CONVERSION_CONSTANT + 3)
+ & 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 ssize_t ltc6373_read_powerdown(struct iio_dev *indio_dev,
+ uintptr_t private,
+ const struct iio_chan_spec *chan,
+ char *buf)
+{
+ struct hmc425a_state *st = iio_priv(indio_dev);
+
+ return sysfs_emit(buf, "%d\n", st->powerdown);
+}
+
+static ssize_t ltc6373_write_powerdown(struct iio_dev *indio_dev,
+ uintptr_t private,
+ const struct iio_chan_spec *chan,
+ const char *buf,
+ size_t len)
+{
+ struct hmc425a_state *st = iio_priv(indio_dev);
+ bool powerdown;
+ int code, ret;
+
+ ret = kstrtobool(buf, &powerdown);
+ if (ret)
+ return ret;
+
+ mutex_lock(&st->lock);
+ st->powerdown = powerdown;
+ code = (powerdown) ? LTC6373_SHUTDOWN : st->gain;
+ ret = hmc425a_write(indio_dev, code);
+ mutex_unlock(&st->lock);
+ return len;
+}
+
+static const struct iio_chan_spec_ext_info ltc6373_ext_info[] = {
+ {
+ .name = "powerdown",
+ .read = ltc6373_read_powerdown,
+ .write = ltc6373_write_powerdown,
+ .shared = IIO_SEPARATE,
+ },
+ {},
+};
+
#define HMC425A_CHAN(_channel) \
{ \
.type = IIO_VOLTAGE, \
@@ -183,10 +260,24 @@ 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), \
+ .ext_info = ltc6373_ext_info, \
+}
+
static const struct iio_chan_spec hmc425a_channels[] = {
HMC425A_CHAN(0),
};

+static const struct iio_chan_spec ltc6373_channels[] = {
+ LTC6373_CHAN(0),
+};
+
static struct hmc425a_chip_info hmc425a_chip_info_tbl[] = {
[ID_HMC425A] = {
.name = "hmc425a",
@@ -215,6 +306,18 @@ 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_MIN_GAIN_CODE,
+ .powerdown_val = LTC6373_SHUTDOWN,
+ .has_powerdown = true,
+ },
+
};

/* Match table for of_platform binding */
@@ -225,6 +328,8 @@ static const struct of_device_id hmc425a_of_match[] = {
.data = &hmc425a_chip_info_tbl[ID_HMC540S]},
{ .compatible = "adi,adrf5740",
.data = &hmc425a_chip_info_tbl[ID_ADRF5740]},
+ { .compatible = "adi,ltc6373",
+ .data = &hmc425a_chip_info_tbl[ID_LTC6373]},
{},
};
MODULE_DEVICE_TABLE(of, hmc425a_of_match);
@@ -270,8 +375,13 @@ static int hmc425a_probe(struct platform_device *pdev)
indio_dev->info = &hmc425a_info;
indio_dev->modes = INDIO_DIRECT_MODE;

- /* Set default gain */
- hmc425a_write(indio_dev, st->gain);
+ if (st->chip_info->has_powerdown) {
+ st->powerdown = true;
+ hmc425a_write(indio_dev, st->chip_info->powerdown_val);
+ } else {
+ /* Set default gain */
+ hmc425a_write(indio_dev, st->gain);
+ }

return devm_iio_device_register(&pdev->dev, indio_dev);
}
--
2.42.0