iio: amplifiers: hmc425a: add support for LTC6373 Instrumentation Amplifier

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>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240220153553.2432-6-mitrutzceclan@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/amplifiers/hmc425a.c b/drivers/iio/amplifiers/hmc425a.c
index 31e495e65dcbe44201723eae1728ffbad6c5caf5..2ee4c0d70281e24c1c818249b86d89ebe06d4876 100644 (file)
--- 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, 2024 Analog Devices Inc.
  */
 
+#include <linux/bits.h>
 #include <linux/bitops.h>
 #include <linux/device.h>
 #include <linux/err.h>
@@ -12,6 +13,7 @@
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
 #include <linux/kernel.h>
+#include <linux/math.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
@@ -20,10 +22,24 @@
 #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 +50,8 @@ struct hmc425a_chip_info {
        int                             gain_min;
        int                             gain_max;
        int                             default_gain;
+       int                             powerdown_val;
+       bool                            has_powerdown;
 
        int                             (*gain_dB_to_code)(int gain, int *code);
        int                             (*code_to_gain_dB)(int code, int *val, int *val2);
@@ -44,6 +62,7 @@ struct hmc425a_state {
        const struct    hmc425a_chip_info *chip_info;
        struct  gpio_descs *gpios;
        u32     gain;
+       bool    powerdown;
 };
 
 static int gain_dB_to_code(struct hmc425a_state *st, int val, int val2, int *code)
@@ -58,6 +77,8 @@ static int gain_dB_to_code(struct hmc425a_state *st, int val, int val2, int *cod
 
        if (gain > inf->gain_max || gain < inf->gain_min)
                return -EINVAL;
+       if (st->powerdown)
+               return -EPERM;
 
        return st->chip_info->gain_dB_to_code(gain, code);
 }
@@ -83,8 +104,17 @@ static int adrf5740_gain_dB_to_code(int gain, int *code)
        return 0;
 }
 
+static int ltc6373_gain_dB_to_code(int gain, int *code)
+{
+       *code = ~(DIV_ROUND_CLOSEST(gain, LTC6373_CONVERSION_CONSTANT) + 3)
+               & LTC6373_CONVERSION_MASK;
+       return 0;
+}
+
 static int code_to_gain_dB(struct hmc425a_state *st, int *val, int *val2)
 {
+       if (st->powerdown)
+               return -EPERM;
        return st->chip_info->code_to_gain_dB(st->gain, val, val2);
 }
 
@@ -114,6 +144,16 @@ static int adrf5740_code_to_gain_dB(int code, int *val, int *val2)
        return 0;
 }
 
+static int ltc6373_code_to_gain_dB(int code, int *val, int *val2)
+{
+       int gain = ((~code & LTC6373_CONVERSION_MASK) - 3) *
+                  LTC6373_CONVERSION_CONSTANT;
+
+       *val = gain / 1000;
+       *val2 = (gain % 1000) * 1000;
+       return 0;
+}
+
 static int hmc425a_write(struct iio_dev *indio_dev, u32 value)
 {
        struct hmc425a_state *st = iio_priv(indio_dev);
@@ -192,6 +232,48 @@ 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;
+       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,                                            \
@@ -201,10 +283,24 @@ 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 const struct hmc425a_chip_info hmc425a_chip_info_tbl[] = {
        [ID_HMC425A] = {
                .name = "hmc425a",
@@ -239,6 +335,19 @@ static const struct hmc425a_chip_info hmc425a_chip_info_tbl[] = {
                .gain_dB_to_code = adrf5740_gain_dB_to_code,
                .code_to_gain_dB = adrf5740_code_to_gain_dB,
        },
+       [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,
+               .gain_dB_to_code = ltc6373_gain_dB_to_code,
+               .code_to_gain_dB = ltc6373_code_to_gain_dB,
+       },
 };
 
 static int hmc425a_probe(struct platform_device *pdev)
@@ -279,8 +388,13 @@ 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);
 }
@@ -293,6 +407,8 @@ 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);