[PATCH v3 0/4] Add LTC2495 support

[PATCH v3 0/4] Add LTC2495 support

[Yusuf Alper Bilgin]

Hi All,

This is the v3 of the patch series adding support for the LTC2495 ADC in
the ltc2497 driver, and enabling the internal temperature channel for
the LTC2495 and LTC2499.

Thanks to Andy Shevchenko for his quick, helpful, and continued review
of the previous version.

In response to the request to check for code size changes, I have run
`bloat-o-meter`. The results confirm no meaningful impact on code size.

Full bloat-o-meter output:
```
./scripts/bloat-o-meter \
    before_patch_4/ltc2497-core.o drivers/iio/adc/ltc2497-core.o
add/remove: 0/0 grow/shrink: 1/1 up/down: 1/-1 (0)
Function                      old     new   delta
ltc2497core_read_raw          413     414      +1
ltc2497core_probe             374     373      -1
Total: Before=11576, After=11576, chg +0.00%

./scripts/bloat-o-meter \
    before_patch_4/ltc2497.o drivers/iio/adc/ltc2497.o
add/remove: 0/0 grow/shrink: 2/0 up/down: 2/0 (2)
Function                      old     new   delta
ltc2497_result_and_measure    275     276      +1
ltc2497_probe                 158     159      +1
Total: Before=1946, After=1948, chg +0.10%

./scripts/bloat-o-meter \
    before_patch_4/ltc2496.o drivers/iio/adc/ltc2496.o
add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0 (0)
Function                      old     new   delta
Total: Before=1251, After=1251, chg +0.00%
```

Best Regards,

Alper

Signed-off-by: Yusuf Alper Bilgin <y.alperbilgin@gmail.com>
---
Changes in v3:
  - Used the standard `kelvin_to_celsius()` helper instead of a custom
    define.
  - Corrected macro definition style.
  - Renamed `LTC2497_CHANNELS` and `LTC_T_CHAN` for clarity.
  - Combined all struct layout optimizations into a single patch.
  - Link to v2: https://lore.kernel.org/r/20250813-ltc2495-v2-0-bbaf20f6ba07@gmail.com

Changes in v2:
  - Rewrote all commit messages to use the imperative mood.
  - Added a justification for the new compatible string to the device
    tree binding commit message.
  - Removed all unrelated whitespace and formatting changes.
  - Removed redundant explicit `false` initializers from structs.
  - Replaced the magic number for Kelvin conversion with a define.
  - Improved comments for defines and temperature scaling constants.
  - Renamed confusing macros and struct fields to be more descriptive.
  - Replaced dynamic channel allocation with a static array approach
    using a shared macro to improve readability.
  - Optimized data structure layouts based on pahole output to remove
    memory holes.
  - Link to v1: https://lore.kernel.org/r/20250812-ltc2495-v1-0-7bf4c6feec2e@gmail.com
---
Implementation Notes
 - checkpatch warning: The new static array approach uses a shared macro
   for the common channels (`LTC2497_CHANNELS`), which triggers a
   checkpatch.pl warning: "Macros with complex values should be enclosed
   in parentheses". However, this will cause a compilitaion error, as an
   initializer list cannot be parenthesized.
 - uV to mV conversion: I could not find a standard macro, so a manual
   division is used for now. This could be a point of future
   improvement.

---
Yusuf Alper Bilgin (4):
      dt-bindings: iio: adc: ltc2497: add lltc,ltc2495 bindings
      iio: adc: ltc2497: add support for LTC2495
      iio: adc: ltc2497: add temperature sensor support
      iio: adc: ltc2497: reorder struct members to fix memory holes

 .../devicetree/bindings/iio/adc/lltc,ltc2497.yaml  |   3 +
 drivers/iio/adc/ltc2497-core.c                     | 141 +++++++++++++++------
 drivers/iio/adc/ltc2497.c                          |  35 ++++-
 drivers/iio/adc/ltc2497.h                          |  23 +++-
 4 files changed, 159 insertions(+), 43 deletions(-)
---
base-commit: acbbb5a20971089064ca6b271dd251e629be8d4d
change-id: 20250811-ltc2495-572817c13fd3

Best regards,
-- 
Yusuf Alper Bilgin <y.alperbilgin@gmail.com>

[PATCH v3 1/4] dt-bindings: iio: adc: ltc2497: add lltc,ltc2495 bindings

[Yusuf Alper Bilgin]

Update the binding documentation for LTC2497 to include LTC2495 to
enable support for its internal temperature sensor, which requires a
different I2C command format and a new IIO channel.

Signed-off-by: Yusuf Alper Bilgin <y.alperbilgin@gmail.com>
---
 Documentation/devicetree/bindings/iio/adc/lltc,ltc2497.yaml | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/adc/lltc,ltc2497.yaml b/Documentation/devicetree/bindings/iio/adc/lltc,ltc2497.yaml
index 5cc6a96840778473895f436b7e2627d6240b254b..2a3e3dcc6ca7a48a0fccb88d8d42fee34efcff73 100644
--- a/Documentation/devicetree/bindings/iio/adc/lltc,ltc2497.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/lltc,ltc2497.yaml
@@ -17,11 +17,13 @@ description: |
 
     https://www.analog.com/media/en/technical-documentation/data-sheets/2309fd.pdf
 
+  LTC2495:
   LTC2497:
   LTC2499:
     16bit ADC supporting up to 16 single ended or 8 differential inputs.
     I2C interface.
 
+    https://www.analog.com/media/en/technical-documentation/data-sheets/2495fe.pdf
     https://www.analog.com/media/en/technical-documentation/data-sheets/2497fb.pdf
     https://www.analog.com/media/en/technical-documentation/data-sheets/2499fe.pdf
 
@@ -29,6 +31,7 @@ properties:
   compatible:
     enum:
       - lltc,ltc2309
+      - lltc,ltc2495
       - lltc,ltc2497
       - lltc,ltc2499
 

-- 
2.43.0

[PATCH v3 2/4] iio: adc: ltc2497: add support for LTC2495

[Yusuf Alper Bilgin]

Update the LTC2497 driver to also support the LTC2495.

Signed-off-by: Yusuf Alper Bilgin <y.alperbilgin@gmail.com>
---
 drivers/iio/adc/ltc2497.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
index eb9d521e86e54def0493ea0e81f63b37900c56a5..8f4665547b5b0d32084599f8557c40102c37a4ce 100644
--- a/drivers/iio/adc/ltc2497.c
+++ b/drivers/iio/adc/ltc2497.c
@@ -19,6 +19,7 @@
 #include "ltc2497.h"
 
 enum ltc2497_chip_type {
+	TYPE_LTC2495,
 	TYPE_LTC2497,
 	TYPE_LTC2499,
 };
@@ -131,6 +132,10 @@ static void ltc2497_remove(struct i2c_client *client)
 }
 
 static const struct ltc2497_chip_info ltc2497_info[] = {
+	[TYPE_LTC2495] = {
+		.resolution = 16,
+		.name = "ltc2495",
+	},
 	[TYPE_LTC2497] = {
 		.resolution = 16,
 		.name = NULL,
@@ -142,6 +147,7 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
 };
 
 static const struct i2c_device_id ltc2497_id[] = {
+	{ "ltc2495", (kernel_ulong_t)&ltc2497_info[TYPE_LTC2495] },
 	{ "ltc2497", (kernel_ulong_t)&ltc2497_info[TYPE_LTC2497] },
 	{ "ltc2499", (kernel_ulong_t)&ltc2497_info[TYPE_LTC2499] },
 	{ }
@@ -149,6 +155,7 @@ static const struct i2c_device_id ltc2497_id[] = {
 MODULE_DEVICE_TABLE(i2c, ltc2497_id);
 
 static const struct of_device_id ltc2497_of_match[] = {
+	{ .compatible = "lltc,ltc2495", .data = &ltc2497_info[TYPE_LTC2495] },
 	{ .compatible = "lltc,ltc2497", .data = &ltc2497_info[TYPE_LTC2497] },
 	{ .compatible = "lltc,ltc2499", .data = &ltc2497_info[TYPE_LTC2499] },
 	{ }

-- 
2.43.0

[PATCH v3 3/4] iio: adc: ltc2497: add temperature sensor support

[Yusuf Alper Bilgin]

Support for reading the internal temperature sensor on LTC2495 and
LTC2499 via a standard IIO temperature channel.

Signed-off-by: Yusuf Alper Bilgin <y.alperbilgin@gmail.com>
---
 drivers/iio/adc/ltc2497-core.c | 141 ++++++++++++++++++++++++++++++-----------
 drivers/iio/adc/ltc2497.c      |  28 +++++++-
 drivers/iio/adc/ltc2497.h      |  15 +++++
 3 files changed, 145 insertions(+), 39 deletions(-)

diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c
index 2dc5c704426949a4ec62c42591d6c2c40ffb79cc..bbb7948f81933ee35103e37cb2ba94354f61b32e 100644
--- a/drivers/iio/adc/ltc2497-core.c
+++ b/drivers/iio/adc/ltc2497-core.c
@@ -12,6 +12,7 @@
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/regulator/consumer.h>
+#include <linux/units.h>
 
 #include "ltc2497.h"
 
@@ -95,10 +96,53 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev,
 		if (ret < 0)
 			return ret;
 
-		*val = ret / 1000;
-		*val2 = ddata->chip_info->resolution + 1;
+		switch (chan->type) {
+		case IIO_VOLTAGE:
+			*val = ret / 1000;
+			*val2 = ddata->chip_info->resolution + 1;
+
+			return IIO_VAL_FRACTIONAL_LOG2;
+
+		case IIO_TEMP:
+			if (!ddata->chip_info->has_temp_channel)
+				return -EINVAL;
+
+			/*
+			 * The datasheet formula to get Temperature in Celsius is:
+			 * Temp_C = (DATAOUT * Vref_V / temp_scale) - 273
+			 *
+			 * To match the IIO framework's model of (raw + offset) * scale,
+			 * and to get the final result in millidegrees Celsius:
+			 *
+			 * Temp_mC = ((DATAOUT * Vref_mV / temp_scale_mV) - 273) * 1000
+			 * Temp_mC = (DATAOUT - (273 * temp_scale_mV / Vref_mv)) * 1000 *
+			 *           Vref_mV / temp_scale_mV
+			 *
+			 * This gives us:
+			 * scale  = Vref_mV * 1000 / temp_scale_mV
+			 * offset = -273 * temp_scale / Vref_mV
+			 */
+			*val = ret;
+			*val2 = ddata->chip_info->temp_scale_mV;
+
+			return IIO_VAL_FRACTIONAL;
+
+		default:
+			return -EINVAL;
+		}
+	case IIO_CHAN_INFO_OFFSET:
+		if (chan->type != IIO_TEMP)
+			return -EINVAL;
+
+		/* see the calculation above. Offset with (-273 * temp_scale / Vref) */
+		ret = regulator_get_voltage(ddata->ref);
+		if (ret < 0)
+			return ret;
 
-		return IIO_VAL_FRACTIONAL_LOG2;
+		*val = kelvin_to_celsius(0) * ddata->chip_info->temp_scale_mV;
+		*val2 = ret / 1000;
+
+		return IIO_VAL_FRACTIONAL;
 
 	default:
 		return -EINVAL;
@@ -126,39 +170,56 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev,
 	.differential = 1, \
 }
 
+#define LTC2497_TEMPERATURE_CHAN \
+{												\
+	.type = IIO_TEMP,									\
+	.channel = 0,										\
+	.address = (LTC2497_ENABLE_TEMPERATURE_CONV),						\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),						\
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),	\
+}
+
+#define LTC2497_VOLTAGE_CHANNEL_LIST \
+	LTC2497_CHAN(0, LTC2497_SGL, "CH0"),			\
+	LTC2497_CHAN(1, LTC2497_SGL, "CH1"),			\
+	LTC2497_CHAN(2, LTC2497_SGL, "CH2"),			\
+	LTC2497_CHAN(3, LTC2497_SGL, "CH3"),			\
+	LTC2497_CHAN(4, LTC2497_SGL, "CH4"),			\
+	LTC2497_CHAN(5, LTC2497_SGL, "CH5"),			\
+	LTC2497_CHAN(6, LTC2497_SGL, "CH6"),			\
+	LTC2497_CHAN(7, LTC2497_SGL, "CH7"),			\
+	LTC2497_CHAN(8, LTC2497_SGL, "CH8"),			\
+	LTC2497_CHAN(9, LTC2497_SGL, "CH9"),			\
+	LTC2497_CHAN(10, LTC2497_SGL, "CH10"),			\
+	LTC2497_CHAN(11, LTC2497_SGL, "CH11"),			\
+	LTC2497_CHAN(12, LTC2497_SGL, "CH12"),			\
+	LTC2497_CHAN(13, LTC2497_SGL, "CH13"),			\
+	LTC2497_CHAN(14, LTC2497_SGL, "CH14"),			\
+	LTC2497_CHAN(15, LTC2497_SGL, "CH15"),			\
+	LTC2497_CHAN_DIFF(0, LTC2497_DIFF),			\
+	LTC2497_CHAN_DIFF(1, LTC2497_DIFF),			\
+	LTC2497_CHAN_DIFF(2, LTC2497_DIFF),			\
+	LTC2497_CHAN_DIFF(3, LTC2497_DIFF),			\
+	LTC2497_CHAN_DIFF(4, LTC2497_DIFF),			\
+	LTC2497_CHAN_DIFF(5, LTC2497_DIFF),			\
+	LTC2497_CHAN_DIFF(6, LTC2497_DIFF),			\
+	LTC2497_CHAN_DIFF(7, LTC2497_DIFF),			\
+	LTC2497_CHAN_DIFF(0, LTC2497_DIFF | LTC2497_SIGN),	\
+	LTC2497_CHAN_DIFF(1, LTC2497_DIFF | LTC2497_SIGN),	\
+	LTC2497_CHAN_DIFF(2, LTC2497_DIFF | LTC2497_SIGN),	\
+	LTC2497_CHAN_DIFF(3, LTC2497_DIFF | LTC2497_SIGN),	\
+	LTC2497_CHAN_DIFF(4, LTC2497_DIFF | LTC2497_SIGN),	\
+	LTC2497_CHAN_DIFF(5, LTC2497_DIFF | LTC2497_SIGN),	\
+	LTC2497_CHAN_DIFF(6, LTC2497_DIFF | LTC2497_SIGN),	\
+	LTC2497_CHAN_DIFF(7, LTC2497_DIFF | LTC2497_SIGN)
+
 static const struct iio_chan_spec ltc2497core_channel[] = {
-	LTC2497_CHAN(0, LTC2497_SGL, "CH0"),
-	LTC2497_CHAN(1, LTC2497_SGL, "CH1"),
-	LTC2497_CHAN(2, LTC2497_SGL, "CH2"),
-	LTC2497_CHAN(3, LTC2497_SGL, "CH3"),
-	LTC2497_CHAN(4, LTC2497_SGL, "CH4"),
-	LTC2497_CHAN(5, LTC2497_SGL, "CH5"),
-	LTC2497_CHAN(6, LTC2497_SGL, "CH6"),
-	LTC2497_CHAN(7, LTC2497_SGL, "CH7"),
-	LTC2497_CHAN(8, LTC2497_SGL, "CH8"),
-	LTC2497_CHAN(9, LTC2497_SGL, "CH9"),
-	LTC2497_CHAN(10, LTC2497_SGL, "CH10"),
-	LTC2497_CHAN(11, LTC2497_SGL, "CH11"),
-	LTC2497_CHAN(12, LTC2497_SGL, "CH12"),
-	LTC2497_CHAN(13, LTC2497_SGL, "CH13"),
-	LTC2497_CHAN(14, LTC2497_SGL, "CH14"),
-	LTC2497_CHAN(15, LTC2497_SGL, "CH15"),
-	LTC2497_CHAN_DIFF(0, LTC2497_DIFF),
-	LTC2497_CHAN_DIFF(1, LTC2497_DIFF),
-	LTC2497_CHAN_DIFF(2, LTC2497_DIFF),
-	LTC2497_CHAN_DIFF(3, LTC2497_DIFF),
-	LTC2497_CHAN_DIFF(4, LTC2497_DIFF),
-	LTC2497_CHAN_DIFF(5, LTC2497_DIFF),
-	LTC2497_CHAN_DIFF(6, LTC2497_DIFF),
-	LTC2497_CHAN_DIFF(7, LTC2497_DIFF),
-	LTC2497_CHAN_DIFF(0, LTC2497_DIFF | LTC2497_SIGN),
-	LTC2497_CHAN_DIFF(1, LTC2497_DIFF | LTC2497_SIGN),
-	LTC2497_CHAN_DIFF(2, LTC2497_DIFF | LTC2497_SIGN),
-	LTC2497_CHAN_DIFF(3, LTC2497_DIFF | LTC2497_SIGN),
-	LTC2497_CHAN_DIFF(4, LTC2497_DIFF | LTC2497_SIGN),
-	LTC2497_CHAN_DIFF(5, LTC2497_DIFF | LTC2497_SIGN),
-	LTC2497_CHAN_DIFF(6, LTC2497_DIFF | LTC2497_SIGN),
-	LTC2497_CHAN_DIFF(7, LTC2497_DIFF | LTC2497_SIGN),
+	LTC2497_VOLTAGE_CHANNEL_LIST,
+};
+
+static const struct iio_chan_spec ltc2497core_channel_with_temperature[] = {
+	LTC2497_VOLTAGE_CHANNEL_LIST,
+	LTC2497_TEMPERATURE_CHAN,
 };
 
 static const struct iio_info ltc2497core_info = {
@@ -182,8 +243,14 @@ int ltc2497core_probe(struct device *dev, struct iio_dev *indio_dev)
 
 	indio_dev->info = &ltc2497core_info;
 	indio_dev->modes = INDIO_DIRECT_MODE;
-	indio_dev->channels = ltc2497core_channel;
-	indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel);
+
+	if (ddata->chip_info->has_temp_channel) {
+		indio_dev->channels = ltc2497core_channel_with_temperature;
+		indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel_with_temperature);
+	} else {
+		indio_dev->channels = ltc2497core_channel;
+		indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel);
+	}
 
 	ret = ddata->result_and_measure(ddata, LTC2497_CONFIG_DEFAULT, NULL);
 	if (ret < 0)
diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
index 8f4665547b5b0d32084599f8557c40102c37a4ce..07fced79aeead3778964b114d479fdcb643c16df 100644
--- a/drivers/iio/adc/ltc2497.c
+++ b/drivers/iio/adc/ltc2497.c
@@ -86,8 +86,28 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
 			return 0;
 	}
 
-	ret = i2c_smbus_write_byte(st->client,
-				   LTC2497_ENABLE | address);
+	/*
+	 * Chips with temperature sensor support (e.g., LTC2495/LTC2499)
+	 * require a two-byte command format to select any channel.
+	 *
+	 * To read the internal temperature, LTC2497_ENABLE_TEMPERATURE_CONV
+	 * is sent as the second byte. To read a voltage channel, LTC2497_EN2
+	 * is sent, which sets the default configuration: simultaneous 50/60Hz
+	 * rejection, 1x speed, and gain=1.
+	 *
+	 * Chips without this feature use a standard single-byte command.
+	 */
+	if (ddata->chip_info->has_temp_channel) {
+		if (address == LTC2497_ENABLE_TEMPERATURE_CONV)
+			ret = i2c_smbus_write_byte_data(st->client, LTC2497_ENABLE,
+							LTC2497_ENABLE_TEMPERATURE_CONV);
+		else
+			ret = i2c_smbus_write_byte_data(st->client, LTC2497_ENABLE | address,
+							LTC2497_EN2);
+	} else {
+		ret = i2c_smbus_write_byte(st->client, LTC2497_ENABLE | address);
+	}
+
 	if (ret)
 		dev_err(&st->client->dev, "i2c transfer failed: %pe\n",
 			ERR_PTR(ret));
@@ -135,6 +155,8 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
 	[TYPE_LTC2495] = {
 		.resolution = 16,
 		.name = "ltc2495",
+		.has_temp_channel = true,
+		.temp_scale_mV = 12250,
 	},
 	[TYPE_LTC2497] = {
 		.resolution = 16,
@@ -143,6 +165,8 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
 	[TYPE_LTC2499] = {
 		.resolution = 24,
 		.name = "ltc2499",
+		.has_temp_channel = true,
+		.temp_scale_mV = 1570000,
 	},
 };
 
diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
index 64e81c95a3dd05911b6717c09ac0560c9f47f304..65f406bc61c24b912de4beed604a074b3ea9df91 100644
--- a/drivers/iio/adc/ltc2497.h
+++ b/drivers/iio/adc/ltc2497.h
@@ -3,10 +3,25 @@
 #define LTC2497_ENABLE			0xA0
 #define LTC2497_CONFIG_DEFAULT		LTC2497_ENABLE
 #define LTC2497_CONVERSION_TIME_MS	150ULL
+#define LTC2497_EN2			BIT(7)
+/* Enable the internal temperature sensor */
+#define LTC2497_IM                      BIT(6)
+/* Second command byte value to initiate a temperature conversion */
+#define LTC2497_ENABLE_TEMPERATURE_CONV	(LTC2497_EN2 | LTC2497_IM)
 
 struct ltc2497_chip_info {
 	u32 resolution;
 	const char *name;
+	/*
+	 * Represents the datasheet constant from the temperature formula:
+	 * T_Kelvin = (DATAOUT * Vref) / temp_scale, where Vref is in Volts.
+	 *
+	 * To allow the driver to use Vref in millivolts for the calculation
+	 * and also to avoid floating points, this stored value represents the
+	 * datasheet constant scaled by 1000.
+	 */
+	u32 temp_scale_mV;
+	bool has_temp_channel;
 };
 
 struct ltc2497core_driverdata {

-- 
2.43.0

[PATCH v3 4/4] iio: adc: ltc2497: reorder struct members to fix memory holes

[Yusuf Alper Bilgin]

Reorder members in the `ltc2497_chip_info` and `ltc2497core_driverdata`
structs to eliminate memory holes identified by the `pahole` tool.

Confirm via the `bloat-o-meter` that this change has no significant
impact on the final code size:

| Object File     | Total Size Change |
|-----------------|-------------------|
| ltc2497-core.o  | 0 (0.00%)         |
| ltc2497.o       | +2 (+0.10%)       |
| ltc2496.o       | 0 (0.00%)         |

Signed-off-by: Yusuf Alper Bilgin <y.alperbilgin@gmail.com>
---
 drivers/iio/adc/ltc2497.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
index 65f406bc61c24b912de4beed604a074b3ea9df91..578f55efc5c400980fe8bbd2b220aafb222d6f33 100644
--- a/drivers/iio/adc/ltc2497.h
+++ b/drivers/iio/adc/ltc2497.h
@@ -10,8 +10,8 @@
 #define LTC2497_ENABLE_TEMPERATURE_CONV	(LTC2497_EN2 | LTC2497_IM)
 
 struct ltc2497_chip_info {
-	u32 resolution;
 	const char *name;
+	u32 resolution;
 	/*
 	 * Represents the datasheet constant from the temperature formula:
 	 * T_Kelvin = (DATAOUT * Vref) / temp_scale, where Vref is in Volts.
@@ -27,12 +27,12 @@ struct ltc2497_chip_info {
 struct ltc2497core_driverdata {
 	struct regulator *ref;
 	ktime_t	time_prev;
-	/* lock to protect against multiple access to the device */
-	struct mutex lock;
 	const struct ltc2497_chip_info	*chip_info;
-	u8 addr_prev;
 	int (*result_and_measure)(struct ltc2497core_driverdata *ddata,
 				  u8 address, int *val);
+	/* lock to protect against multiple access to the device */
+	struct mutex lock;
+	u8 addr_prev;
 };
 
 int ltc2497core_probe(struct device *dev, struct iio_dev *indio_dev);

-- 
2.43.0

Re: [PATCH v3 3/4] iio: adc: ltc2497: add temperature sensor support

[David Lechner]

On 8/14/25 6:00 AM, Yusuf Alper Bilgin wrote:
> Support for reading the internal temperature sensor on LTC2495 and
> LTC2499 via a standard IIO temperature channel.
> 
> Signed-off-by: Yusuf Alper Bilgin <y.alperbilgin@gmail.com>
> ---
>  drivers/iio/adc/ltc2497-core.c | 141 ++++++++++++++++++++++++++++++-----------
>  drivers/iio/adc/ltc2497.c      |  28 +++++++-
>  drivers/iio/adc/ltc2497.h      |  15 +++++
>  3 files changed, 145 insertions(+), 39 deletions(-)
> 
> diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c
> index 2dc5c704426949a4ec62c42591d6c2c40ffb79cc..bbb7948f81933ee35103e37cb2ba94354f61b32e 100644
> --- a/drivers/iio/adc/ltc2497-core.c
> +++ b/drivers/iio/adc/ltc2497-core.c
> @@ -12,6 +12,7 @@
>  #include <linux/module.h>
>  #include <linux/mutex.h>
>  #include <linux/regulator/consumer.h>
> +#include <linux/units.h>
>  
>  #include "ltc2497.h"
>  
> @@ -95,10 +96,53 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev,
>  		if (ret < 0)
>  			return ret;
>  
> -		*val = ret / 1000;
> -		*val2 = ddata->chip_info->resolution + 1;
> +		switch (chan->type) {
> +		case IIO_VOLTAGE:
> +			*val = ret / 1000;
> +			*val2 = ddata->chip_info->resolution + 1;
> +
> +			return IIO_VAL_FRACTIONAL_LOG2;
> +
> +		case IIO_TEMP:
> +			if (!ddata->chip_info->has_temp_channel)
> +				return -EINVAL;
> +
> +			/*
> +			 * The datasheet formula to get Temperature in Celsius is:
> +			 * Temp_C = (DATAOUT * Vref_V / temp_scale) - 273
> +			 *
> +			 * To match the IIO framework's model of (raw + offset) * scale,
> +			 * and to get the final result in millidegrees Celsius:
> +			 *
> +			 * Temp_mC = ((DATAOUT * Vref_mV / temp_scale_mV) - 273) * 1000
> +			 * Temp_mC = (DATAOUT - (273 * temp_scale_mV / Vref_mv)) * 1000 *
> +			 *           Vref_mV / temp_scale_mV
> +			 *
> +			 * This gives us:
> +			 * scale  = Vref_mV * 1000 / temp_scale_mV
> +			 * offset = -273 * temp_scale / Vref_mV
> +			 */

Probably don't need quite so much comments here. TBH, I though just the
comment in struct ltc2497_chip_info was enough.

> +			*val = ret;
> +			*val2 = ddata->chip_info->temp_scale_mV;
> +
> +			return IIO_VAL_FRACTIONAL;
> +
> +		default:
> +			return -EINVAL;
> +		}
> +	case IIO_CHAN_INFO_OFFSET:
> +		if (chan->type != IIO_TEMP)
> +			return -EINVAL;
> +
> +		/* see the calculation above. Offset with (-273 * temp_scale / Vref) */
> +		ret = regulator_get_voltage(ddata->ref);
> +		if (ret < 0)
> +			return ret;
>  
> -		return IIO_VAL_FRACTIONAL_LOG2;
> +		*val = kelvin_to_celsius(0) * ddata->chip_info->temp_scale_mV;
> +		*val2 = ret / 1000;
> +
> +		return IIO_VAL_FRACTIONAL;
>  
>  	default:
>  		return -EINVAL;
> @@ -126,39 +170,56 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev,
>  	.differential = 1, \
>  }
>  
> +#define LTC2497_TEMPERATURE_CHAN \
> +{												\
> +	.type = IIO_TEMP,									\
> +	.channel = 0,										\

No need for channel if indexed == 0.

> +	.address = (LTC2497_ENABLE_TEMPERATURE_CONV),						\

Since this can't be used the same was as the voltage address
field, not sure it makes sense to set this. Later, we can
just check the channel.type instead.

> +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),						\
> +	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),	\
> +}
> +
> +#define LTC2497_VOLTAGE_CHANNEL_LIST \
> +	LTC2497_CHAN(0, LTC2497_SGL, "CH0"),			\
> +	LTC2497_CHAN(1, LTC2497_SGL, "CH1"),			\
> +	LTC2497_CHAN(2, LTC2497_SGL, "CH2"),			\
> +	LTC2497_CHAN(3, LTC2497_SGL, "CH3"),			\
> +	LTC2497_CHAN(4, LTC2497_SGL, "CH4"),			\
> +	LTC2497_CHAN(5, LTC2497_SGL, "CH5"),			\
> +	LTC2497_CHAN(6, LTC2497_SGL, "CH6"),			\
> +	LTC2497_CHAN(7, LTC2497_SGL, "CH7"),			\
> +	LTC2497_CHAN(8, LTC2497_SGL, "CH8"),			\
> +	LTC2497_CHAN(9, LTC2497_SGL, "CH9"),			\
> +	LTC2497_CHAN(10, LTC2497_SGL, "CH10"),			\
> +	LTC2497_CHAN(11, LTC2497_SGL, "CH11"),			\
> +	LTC2497_CHAN(12, LTC2497_SGL, "CH12"),			\
> +	LTC2497_CHAN(13, LTC2497_SGL, "CH13"),			\
> +	LTC2497_CHAN(14, LTC2497_SGL, "CH14"),			\
> +	LTC2497_CHAN(15, LTC2497_SGL, "CH15"),			\
> +	LTC2497_CHAN_DIFF(0, LTC2497_DIFF),			\
> +	LTC2497_CHAN_DIFF(1, LTC2497_DIFF),			\
> +	LTC2497_CHAN_DIFF(2, LTC2497_DIFF),			\
> +	LTC2497_CHAN_DIFF(3, LTC2497_DIFF),			\
> +	LTC2497_CHAN_DIFF(4, LTC2497_DIFF),			\
> +	LTC2497_CHAN_DIFF(5, LTC2497_DIFF),			\
> +	LTC2497_CHAN_DIFF(6, LTC2497_DIFF),			\
> +	LTC2497_CHAN_DIFF(7, LTC2497_DIFF),			\
> +	LTC2497_CHAN_DIFF(0, LTC2497_DIFF | LTC2497_SIGN),	\
> +	LTC2497_CHAN_DIFF(1, LTC2497_DIFF | LTC2497_SIGN),	\
> +	LTC2497_CHAN_DIFF(2, LTC2497_DIFF | LTC2497_SIGN),	\
> +	LTC2497_CHAN_DIFF(3, LTC2497_DIFF | LTC2497_SIGN),	\
> +	LTC2497_CHAN_DIFF(4, LTC2497_DIFF | LTC2497_SIGN),	\
> +	LTC2497_CHAN_DIFF(5, LTC2497_DIFF | LTC2497_SIGN),	\
> +	LTC2497_CHAN_DIFF(6, LTC2497_DIFF | LTC2497_SIGN),	\
> +	LTC2497_CHAN_DIFF(7, LTC2497_DIFF | LTC2497_SIGN)
> +
>  static const struct iio_chan_spec ltc2497core_channel[] = {
> -	LTC2497_CHAN(0, LTC2497_SGL, "CH0"),
> -	LTC2497_CHAN(1, LTC2497_SGL, "CH1"),
> -	LTC2497_CHAN(2, LTC2497_SGL, "CH2"),
> -	LTC2497_CHAN(3, LTC2497_SGL, "CH3"),
> -	LTC2497_CHAN(4, LTC2497_SGL, "CH4"),
> -	LTC2497_CHAN(5, LTC2497_SGL, "CH5"),
> -	LTC2497_CHAN(6, LTC2497_SGL, "CH6"),
> -	LTC2497_CHAN(7, LTC2497_SGL, "CH7"),
> -	LTC2497_CHAN(8, LTC2497_SGL, "CH8"),
> -	LTC2497_CHAN(9, LTC2497_SGL, "CH9"),
> -	LTC2497_CHAN(10, LTC2497_SGL, "CH10"),
> -	LTC2497_CHAN(11, LTC2497_SGL, "CH11"),
> -	LTC2497_CHAN(12, LTC2497_SGL, "CH12"),
> -	LTC2497_CHAN(13, LTC2497_SGL, "CH13"),
> -	LTC2497_CHAN(14, LTC2497_SGL, "CH14"),
> -	LTC2497_CHAN(15, LTC2497_SGL, "CH15"),
> -	LTC2497_CHAN_DIFF(0, LTC2497_DIFF),
> -	LTC2497_CHAN_DIFF(1, LTC2497_DIFF),
> -	LTC2497_CHAN_DIFF(2, LTC2497_DIFF),
> -	LTC2497_CHAN_DIFF(3, LTC2497_DIFF),
> -	LTC2497_CHAN_DIFF(4, LTC2497_DIFF),
> -	LTC2497_CHAN_DIFF(5, LTC2497_DIFF),
> -	LTC2497_CHAN_DIFF(6, LTC2497_DIFF),
> -	LTC2497_CHAN_DIFF(7, LTC2497_DIFF),
> -	LTC2497_CHAN_DIFF(0, LTC2497_DIFF | LTC2497_SIGN),
> -	LTC2497_CHAN_DIFF(1, LTC2497_DIFF | LTC2497_SIGN),
> -	LTC2497_CHAN_DIFF(2, LTC2497_DIFF | LTC2497_SIGN),
> -	LTC2497_CHAN_DIFF(3, LTC2497_DIFF | LTC2497_SIGN),
> -	LTC2497_CHAN_DIFF(4, LTC2497_DIFF | LTC2497_SIGN),
> -	LTC2497_CHAN_DIFF(5, LTC2497_DIFF | LTC2497_SIGN),
> -	LTC2497_CHAN_DIFF(6, LTC2497_DIFF | LTC2497_SIGN),
> -	LTC2497_CHAN_DIFF(7, LTC2497_DIFF | LTC2497_SIGN),
> +	LTC2497_VOLTAGE_CHANNEL_LIST,
> +};
> +
> +static const struct iio_chan_spec ltc2497core_channel_with_temperature[] = {
> +	LTC2497_VOLTAGE_CHANNEL_LIST,
> +	LTC2497_TEMPERATURE_CHAN,
>  };
>  
>  static const struct iio_info ltc2497core_info = {
> @@ -182,8 +243,14 @@ int ltc2497core_probe(struct device *dev, struct iio_dev *indio_dev)
>  
>  	indio_dev->info = &ltc2497core_info;
>  	indio_dev->modes = INDIO_DIRECT_MODE;
> -	indio_dev->channels = ltc2497core_channel;
> -	indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel);
> +
> +	if (ddata->chip_info->has_temp_channel) {
> +		indio_dev->channels = ltc2497core_channel_with_temperature;
> +		indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel_with_temperature);
> +	} else {
> +		indio_dev->channels = ltc2497core_channel;
> +		indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel);
> +	}
>  
>  	ret = ddata->result_and_measure(ddata, LTC2497_CONFIG_DEFAULT, NULL);
>  	if (ret < 0)
> diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
> index 8f4665547b5b0d32084599f8557c40102c37a4ce..07fced79aeead3778964b114d479fdcb643c16df 100644
> --- a/drivers/iio/adc/ltc2497.c
> +++ b/drivers/iio/adc/ltc2497.c
> @@ -86,8 +86,28 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
>  			return 0;
>  	}
>  
> -	ret = i2c_smbus_write_byte(st->client,
> -				   LTC2497_ENABLE | address);
> +	/*
> +	 * Chips with temperature sensor support (e.g., LTC2495/LTC2499)
> +	 * require a two-byte command format to select any channel.
> +	 *
> +	 * To read the internal temperature, LTC2497_ENABLE_TEMPERATURE_CONV
> +	 * is sent as the second byte. To read a voltage channel, LTC2497_EN2
> +	 * is sent, which sets the default configuration: simultaneous 50/60Hz
> +	 * rejection, 1x speed, and gain=1.
> +	 *
> +	 * Chips without this feature use a standard single-byte command.
> +	 */
> +	if (ddata->chip_info->has_temp_channel) {
> +		if (address == LTC2497_ENABLE_TEMPERATURE_CONV)

Here we can just check the channel type.

> +			ret = i2c_smbus_write_byte_data(st->client, LTC2497_ENABLE,
> +							LTC2497_ENABLE_TEMPERATURE_CONV);

And use LTC2497_EN2 | LTC2497_IM here.

> +		else
> +			ret = i2c_smbus_write_byte_data(st->client, LTC2497_ENABLE | address,
> +							LTC2497_EN2);
> +	} else {
> +		ret = i2c_smbus_write_byte(st->client, LTC2497_ENABLE | address);
> +	}
> +
>  	if (ret)
>  		dev_err(&st->client->dev, "i2c transfer failed: %pe\n",
>  			ERR_PTR(ret));
> @@ -135,6 +155,8 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
>  	[TYPE_LTC2495] = {
>  		.resolution = 16,
>  		.name = "ltc2495",
> +		.has_temp_channel = true,
> +		.temp_scale_mV = 12250,
>  	},
>  	[TYPE_LTC2497] = {
>  		.resolution = 16,
> @@ -143,6 +165,8 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
>  	[TYPE_LTC2499] = {
>  		.resolution = 24,
>  		.name = "ltc2499",
> +		.has_temp_channel = true,
> +		.temp_scale_mV = 1570000,
>  	},
>  };
>  
> diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
> index 64e81c95a3dd05911b6717c09ac0560c9f47f304..65f406bc61c24b912de4beed604a074b3ea9df91 100644
> --- a/drivers/iio/adc/ltc2497.h
> +++ b/drivers/iio/adc/ltc2497.h
> @@ -3,10 +3,25 @@
>  #define LTC2497_ENABLE			0xA0
>  #define LTC2497_CONFIG_DEFAULT		LTC2497_ENABLE
>  #define LTC2497_CONVERSION_TIME_MS	150ULL
> +#define LTC2497_EN2			BIT(7)
> +/* Enable the internal temperature sensor */
> +#define LTC2497_IM                      BIT(6)

These should go directly above:

#define LTC2497_SGL			BIT(4)

in the .c file. No need to have them in the header.


> +/* Second command byte value to initiate a temperature conversion */
> +#define LTC2497_ENABLE_TEMPERATURE_CONV	(LTC2497_EN2 | LTC2497_IM)

This macro seems odd. We usually don't make macros for combined bits
like this. And the way it is being used in the code feels a bit odd
as well. We can probably rework the code to not need it as suggested
in some of the comments above.

>  
>  struct ltc2497_chip_info {
>  	u32 resolution;
>  	const char *name;
> +	/*
> +	 * Represents the datasheet constant from the temperature formula:
> +	 * T_Kelvin = (DATAOUT * Vref) / temp_scale, where Vref is in Volts.
> +	 *
> +	 * To allow the driver to use Vref in millivolts for the calculation
> +	 * and also to avoid floating points, this stored value represents the
> +	 * datasheet constant scaled by 1000.
> +	 */
> +	u32 temp_scale_mV;
> +	bool has_temp_channel;
>  };
>  
>  struct ltc2497core_driverdata {
> 

Re: [PATCH v3 3/4] iio: adc: ltc2497: add temperature sensor support

[Krzysztof Kozlowski]

On Thu, Aug 14, 2025 at 01:00:19PM +0200, Yusuf Alper Bilgin wrote:
> Support for reading the internal temperature sensor on LTC2495 and
> LTC2499 via a standard IIO temperature channel.
> 
> Signed-off-by: Yusuf Alper Bilgin <y.alperbilgin@gmail.com>
> ---
>  drivers/iio/adc/ltc2497-core.c | 141 ++++++++++++++++++++++++++++++-----------
>  drivers/iio/adc/ltc2497.c      |  28 +++++++-
>  drivers/iio/adc/ltc2497.h      |  15 +++++

Thus should be squashed with previous patch, otherwise previous patch is
just incomplete and broken. Unless... your binding is incorrect (I will
comment there).

Best regards,
Krzysztof

Re: [PATCH v3 1/4] dt-bindings: iio: adc: ltc2497: add lltc,ltc2495 bindings

[Krzysztof Kozlowski]

On Thu, Aug 14, 2025 at 01:00:17PM +0200, Yusuf Alper Bilgin wrote:
> Update the binding documentation for LTC2497 to include LTC2495 to
> enable support for its internal temperature sensor, which requires a
> different I2C command format and a new IIO channel.

Your patch #2 says they are compatible, so either this patch is wrong
(and you are supposed to use fallbacks) or patch #2 is wrong/incomplete.

Best regards,
Krzysztof

Re: [PATCH v3 1/4] dt-bindings: iio: adc: ltc2497: add lltc,ltc2495 bindings

[Jonathan Cameron]

On Fri, 15 Aug 2025 10:57:21 +0200
Krzysztof Kozlowski <krzk@kernel.org> wrote:

> On Thu, Aug 14, 2025 at 01:00:17PM +0200, Yusuf Alper Bilgin wrote:
> > Update the binding documentation for LTC2497 to include LTC2495 to
> > enable support for its internal temperature sensor, which requires a
> > different I2C command format and a new IIO channel.  
> 
> Your patch #2 says they are compatible, so either this patch is wrong
> (and you are supposed to use fallbacks) or patch #2 is wrong/incomplete.
Agreed.  Going too fast here, and discussion on v1 wasn't finished.

Jonathan

> 
> Best regards,
> Krzysztof
>