[PATCH 0/3] Add support for LTC6373

[PATCH 0/3] Add support for LTC6373

[Dumitru Ceclan]

This patch series adds support for the LTC6373 Instrumentation Amplifier within
the existing HMC425A driver.

The LTC6373 is a silicon, 3-bit Fully-Differential digital instrumentation
amplifier that supports the following programmable gains (Vout/Vin):
 G = 0.25, 0.5, 1, 2, 4, 8, 16 + Shutdown.
The programmable interface consists of 3 digitally controled inputs.

Dumitru Ceclan (3):
  dt-bindings: iio: hmc425a: add entry for LTC6373
  iio: amplifiers: hmc425a: move conversion logic
  iio: amplifiers: hmc425a: add support for LTC6373 Instrumentation
    Amplifier

 .../bindings/iio/amplifiers/adi,hmc425a.yaml  |  16 ++
 drivers/iio/amplifiers/hmc425a.c              | 178 +++++++++++++-----
 2 files changed, 149 insertions(+), 45 deletions(-)

-- 
2.42.0

[PATCH 1/3] dt-bindings: iio: hmc425a: add entry for LTC6373

[Dumitru Ceclan]

The LTC6373 is a silicon, 3-bit Fully-Differential digital instrumentation
amplifier that supports the following programmable gains (Vout/Vin):
 G = 0.25, 0.5, 1, 2, 4, 8, 16 + Shutdown.

Signed-off-by: Dumitru Ceclan <mitrutzceclan@gmail.com>
---
 .../bindings/iio/amplifiers/adi,hmc425a.yaml     | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/amplifiers/adi,hmc425a.yaml b/Documentation/devicetree/bindings/iio/amplifiers/adi,hmc425a.yaml
index 67de9d4e3a1d..8e7d99823059 100644
--- a/Documentation/devicetree/bindings/iio/amplifiers/adi,hmc425a.yaml
+++ b/Documentation/devicetree/bindings/iio/amplifiers/adi,hmc425a.yaml
@@ -21,6 +21,8 @@ description: |
   HMC540S 1 dB LSB Silicon MMIC 4-Bit Digital Positive Control Attenuator, 0.1 - 8 GHz
     https://www.analog.com/media/en/technical-documentation/data-sheets/hmc540s.pdf
 
+  LTC6373 is a 3-Bit precision instrumentation amplifier with fully differential outputs
+    https://www.analog.com/media/en/technical-documentation/data-sheets/ltc6373.pdf
 
 properties:
   compatible:
@@ -28,6 +30,7 @@ properties:
       - adi,adrf5740
       - adi,hmc425a
       - adi,hmc540s
+      - adi,ltc6373
 
   vcc-supply: true
 
@@ -38,6 +41,19 @@ properties:
     minItems: 6
     maxItems: 6
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: adi,ltc6373
+
+    then:
+      properties:
+        ctrl-gpios:
+          minItems: 3
+          maxItems: 3
+
 required:
   - compatible
   - ctrl-gpios
-- 
2.42.0

Re: [PATCH 1/3] dt-bindings: iio: hmc425a: add entry for LTC6373

[Krzysztof Kozlowski]

On 21/12/2023 12:38, Dumitru Ceclan wrote:
>  
> +allOf:
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            const: adi,ltc6373
> +
> +    then:
> +      properties:
> +        ctrl-gpios:
> +          minItems: 3
> +          maxItems: 3

Test your DTS first. This leads to errors. :(
You miss minItems top-level and here else:.

Best regards,
Krzysztof

[PATCH 2/3] iio: amplifiers: hmc425a: move conversion logic

[Dumitru Ceclan]

Move gain-dB<->code conversion logic from read_raw and write_raw to
hmc425a_gain_dB_to_code() and hmc425a_code_to_gain_dB().

Signed-off-by: Dumitru Ceclan <mitrutzceclan@gmail.com>
---
 drivers/iio/amplifiers/hmc425a.c | 100 ++++++++++++++++++-------------
 1 file changed, 57 insertions(+), 43 deletions(-)

diff --git a/drivers/iio/amplifiers/hmc425a.c b/drivers/iio/amplifiers/hmc425a.c
index ed4d72922696..b5fd19403d15 100644
--- a/drivers/iio/amplifiers/hmc425a.c
+++ b/drivers/iio/amplifiers/hmc425a.c
@@ -56,35 +56,70 @@ static int hmc425a_write(struct iio_dev *indio_dev, u32 value)
 	return 0;
 }
 
+static int hmc425a_gain_dB_to_code(struct hmc425a_state *st, int val, int val2, int *code)
+{
+	struct hmc425a_chip_info *inf = st->chip_info;
+	int gain, temp;
+
+	if (val < 0)
+		gain = (val * 1000) - (val2 / 1000);
+	else
+		gain = (val * 1000) + (val2 / 1000);
+
+	if (gain > inf->gain_max || gain < inf->gain_min)
+		return -EINVAL;
+
+	switch (st->type) {
+	case ID_HMC425A:
+		*code = ~((abs(gain) / 500) & 0x3F);
+		break;
+	case ID_HMC540S:
+		*code = ~((abs(gain) / 1000) & 0xF);
+		break;
+	case ID_ADRF5740:
+		temp = (abs(gain) / 2000) & 0xF;
+		*code = temp & BIT(3) ? temp | BIT(2) : temp;
+		break;
+	}
+	return 0;
+}
+
+static int hmc425a_code_to_gain_dB(struct hmc425a_state *st, int *val, int *val2)
+{
+	int code, gain;
+
+	code = st->gain;
+	switch (st->type) {
+	case ID_HMC425A:
+		gain = ~code * -500;
+		break;
+	case ID_HMC540S:
+		gain = ~code * -1000;
+		break;
+	case ID_ADRF5740:
+		code = code & BIT(3) ? code & ~BIT(2) : code;
+		gain = code * -2000;
+		break;
+	}
+
+	*val = gain / 1000;
+	*val2 = (gain % 1000) * 1000;
+	return 0;
+}
+
 static int hmc425a_read_raw(struct iio_dev *indio_dev,
 			    struct iio_chan_spec const *chan, int *val,
 			    int *val2, long m)
 {
 	struct hmc425a_state *st = iio_priv(indio_dev);
-	int code, gain = 0;
 	int ret;
 
 	mutex_lock(&st->lock);
 	switch (m) {
 	case IIO_CHAN_INFO_HARDWAREGAIN:
-		code = st->gain;
-
-		switch (st->type) {
-		case ID_HMC425A:
-			gain = ~code * -500;
-			break;
-		case ID_HMC540S:
-			gain = ~code * -1000;
-			break;
-		case ID_ADRF5740:
-			code = code & BIT(3) ? code & ~BIT(2) : code;
-			gain = code * -2000;
+		ret = hmc425a_code_to_gain_dB(st, val, val2);
+		if (ret)
 			break;
-		}
-
-		*val = gain / 1000;
-		*val2 = (gain % 1000) * 1000;
-
 		ret = IIO_VAL_INT_PLUS_MICRO_DB;
 		break;
 	default:
@@ -100,36 +135,15 @@ static int hmc425a_write_raw(struct iio_dev *indio_dev,
 			     int val2, long mask)
 {
 	struct hmc425a_state *st = iio_priv(indio_dev);
-	struct hmc425a_chip_info *inf = st->chip_info;
-	int code = 0, gain;
-	int ret;
-
-	if (val < 0)
-		gain = (val * 1000) - (val2 / 1000);
-	else
-		gain = (val * 1000) + (val2 / 1000);
-
-	if (gain > inf->gain_max || gain < inf->gain_min)
-		return -EINVAL;
-
-	switch (st->type) {
-	case ID_HMC425A:
-		code = ~((abs(gain) / 500) & 0x3F);
-		break;
-	case ID_HMC540S:
-		code = ~((abs(gain) / 1000) & 0xF);
-		break;
-	case ID_ADRF5740:
-		code = (abs(gain) / 2000) & 0xF;
-		code = code & BIT(3) ? code | BIT(2) : code;
-		break;
-	}
+	int code = 0, ret;
 
 	mutex_lock(&st->lock);
 	switch (mask) {
 	case IIO_CHAN_INFO_HARDWAREGAIN:
+		ret = hmc425a_gain_dB_to_code(st, val, val2, &code);
+		if (ret)
+			break;
 		st->gain = code;
-
 		ret = hmc425a_write(indio_dev, st->gain);
 		break;
 	default:
-- 
2.42.0

[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@gmail.com>
---
 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

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@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>
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@vger.kernel.org
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)