[PATCH v3 0/4] iio: adc: ltc2497: add LTC2493 support and line-frequency rejection

[PATCH v3 0/4] iio: adc: ltc2497: add LTC2493 support and line-frequency rejection

[Andrei Stancovici via B4 Relay]

This series adds LTC2493 support to the ltc2497 driver, and adds FA/FB
line-frequency rejection for the LTC2499 and the LTC2493.

It includes:
- the LTC2493 device-tree binding,
- FA/FB line-frequency rejection (50Hz, 60Hz, or both) exposed via
  filter_mode, implemented in the core and enabled for the LTC2499,
- a preparatory refactor giving each supported channel layout a channel
  set in the core, referenced directly from chip_info,
- LTC2493 support in the driver: 4 single-ended inputs or 2 differential
  pairs, 24-bit result, same command format as the LTC2499, the internal
  PTAT temperature channel, the 2x conversion speed mode exposed via
  sampling_frequency, and the same rejection selection.

The rejection patch also adjusts the conversion wait time for each
rejection mode. The 50Hz-only mode takes up to 163.5 ms at 1x, while the
previous fixed 150 ms delay only covered the default 50/60Hz mode.

Validated on a Raspberry Pi 4 running 7.3.0-rc4, over an IIO network
backend, with a DC1010A-A board (LTC2493), a DC1012A-A board (LTC2499)
and an LTC2497:
- LTC2493: 41/41 hardware tests passed,
- LTC2499: 36/36 hardware tests passed,
- LTC2497: 24/24 hardware tests passed,
- all LTC2493 rejection x speed combinations were exercised without
  conversion or I2C errors.

LTC2496 was build-tested only because no LTC2496 hardware was available.

The source in this series matches the hardware-tested tree.

Signed-off-by: Andrei Stancovici <andrei.stancovici@analog.com>
---
Changes in v3:
- The channel-set selection moved into a preparatory patch, so the patch
  adding the LTC2493 no longer touches the chip_info of the parts
  already supported (Nuno Sá).
- chip_info now references a per-device channel set directly. The
  num_inputs field and the keyed lookup it was matched against in probe
  are both gone (Nuno Sá).
- The LTC2493 patch is reduced to the device-specific additions.
- The binding and FA/FB patches are unchanged. Nuno Sá's Reviewed-by is
  added to the FA/FB patch.
- Behaviour revalidated on hardware on all three parts; see the
  validation summary above.
- Per-patch changelogs are under the --- of each patch.
- Link to v2: https://patch.msgid.link/20261022-submission-ltc2493-support-v1-v2-0-391d908d2877@analog.com

---
Andrei Stancovici (4):
      dt-bindings: iio: adc: lltc,ltc2497: add LTC2493 support
      iio: adc: ltc2497: add FA/FB line-frequency rejection selection
      iio: adc: ltc2497: select the channel set per device
      iio: adc: ltc2497: add LTC2493 support

 .../devicetree/bindings/iio/adc/lltc,ltc2497.yaml  |   7 +
 drivers/iio/adc/ltc2496.c                          |   1 +
 drivers/iio/adc/ltc2497-core.c                     | 208 ++++++++++++++++-----
 drivers/iio/adc/ltc2497.c                          |  47 +++--
 drivers/iio/adc/ltc2497.h                          |  44 ++++-
 5 files changed, 243 insertions(+), 64 deletions(-)
---
base-commit: a3b3580713f3ac5a32dc2874ee546828977a1d68
change-id: 20261009-submission-ltc2493-support-v1-86449ede432d

Best regards,
--  
Andrei Stancovici <andrei.stancovici@analog.com>

[PATCH v3 1/4] dt-bindings: iio: adc: lltc,ltc2497: add LTC2493 support

[Andrei Stancovici via B4 Relay]

From: Andrei Stancovici <andrei.stancovici@analog.com>

The LTC2493 is a 24-bit delta-sigma ADC with 4 single-ended or 2
differential inputs and an I2C interface. Its channel map matches no
part already listed, so it gets its own compatible rather than a
fallback; no new property is needed.

Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Andrei Stancovici <andrei.stancovici@analog.com>

---
Changes in v3:
- No change.
---
 Documentation/devicetree/bindings/iio/adc/lltc,ltc2497.yaml | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/adc/lltc,ltc2497.yaml b/Documentation/devicetree/bindings/iio/adc/lltc,ltc2497.yaml
index 67445ad2bb3b..4df5aadd1e1d 100644
--- a/Documentation/devicetree/bindings/iio/adc/lltc,ltc2497.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/lltc,ltc2497.yaml
@@ -23,6 +23,12 @@ description: |
 
     https://www.analog.com/media/en/technical-documentation/data-sheets/2309fd.pdf
 
+  LTC2493:
+    24bit ADC supporting up to 4 single ended or 2 differential inputs.
+    I2C interface.
+
+    https://www.analog.com/media/en/technical-documentation/data-sheets/2493fe.pdf
+
   LTC2497:
   LTC2499:
     16bit ADC supporting up to 16 single ended or 8 differential inputs.
@@ -36,6 +42,7 @@ properties:
     enum:
       - lltc,ltc2305
       - lltc,ltc2309
+      - lltc,ltc2493
       - lltc,ltc2497
       - lltc,ltc2499
 

-- 
2.43.0

[PATCH v3 2/4] iio: adc: ltc2497: add FA/FB line-frequency rejection selection

[Andrei Stancovici via B4 Relay]

From: Andrei Stancovici <andrei.stancovici@analog.com>

The LTC2499 can suppress mains interference at 50Hz, 60Hz, or
simultaneously at both, which is the power-up default. Expose the
selection through filter_mode and filter_mode_available. It applies to
voltage and temperature conversions alike, so the attribute is
device-wide.

The rejection mode also sets the conversion time and the output rate, so
both are now tracked per mode. 50Hz-only rejection takes up to 163.5 ms
at 1x, which the previous 150 ms budget did not cover; a read in that
mode could reprogram the device mid-conversion and fail with -EIO.

Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/2499fa.pdf
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Andrei Stancovici <andrei.stancovici@analog.com>

---
Changes in v3:
- No change.
- The guard(mutex) and mutex_lock() mix noted on v2 is left to a
  separate follow-up series, keeping to the scope limit set on v1.
---
 drivers/iio/adc/ltc2497-core.c | 161 ++++++++++++++++++++++++++++++++---------
 drivers/iio/adc/ltc2497.c      |  34 +++++----
 drivers/iio/adc/ltc2497.h      |  30 ++++++--
 3 files changed, 170 insertions(+), 55 deletions(-)

diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c
index a6e34da83b81..c218d87d3a62 100644
--- a/drivers/iio/adc/ltc2497-core.c
+++ b/drivers/iio/adc/ltc2497-core.c
@@ -6,7 +6,10 @@
  * Copyright (C) 2017 Analog Devices Inc.
  */
 
+#include <linux/cleanup.h>
 #include <linux/delay.h>
+#include <linux/device/devres.h>
+#include <linux/gfp.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/driver.h>
 #include <linux/math64.h>
@@ -22,19 +25,24 @@
 #define LTC2497_SIGN			BIT(3)
 
 /*
- * Output-rate modes, indexed by ltc2497core_driverdata.speed_2x
- * (0 = 1x, the power-on default; 1 = 2x, LTC2499 only).  The advertised
- * sampling_frequency and the conversion-time budget are two views of the same
- * mode, so they are kept in lock-step here.
+ * Output-rate modes as [rejection][{1x, 2x}], each a (Hz, microHz) pair taken
+ * as 1 / t_CONV typ for that combination.  The advertised sampling_frequency
+ * and the conversion-time budget are two views of the same mode, so the rows
+ * here are kept in lock-step with ltc2497core_conv_time_ms_tbl.
  */
-static const int ltc2497core_samp_freq_avail[] = {
-	6, 800000,	/* 1x: ~6.8 Hz  (1 / t_CONV_1 typ 146.9ms) */
-	13, 600000,	/* 2x: ~13.6 Hz (1 / t_CONV_2 typ  73.6ms) */
+static const int ltc2497core_samp_freq_avail[][4] = {
+	[LTC2499_REJECT_50_60]	= { 6, 800000, 13, 600000 },
+	[LTC2499_REJECT_50]	= { 6, 240000, 12, 450000 },
+	[LTC2499_REJECT_60]	= { 7, 490000, 14, 950000 },
 };
 
-static const unsigned int ltc2497core_conv_time_ms_tbl[] = {
-	LTC2497_CONV_TIME_1X_MS,		/* 1x */
-	LTC2499_CONV_TIME_2X_MS,		/* 2x */
+static const unsigned int ltc2497core_conv_time_ms_tbl[][2] = {
+	[LTC2499_REJECT_50_60]	= { LTC2497_CONV_TIME_50_60_1X_MS,
+				    LTC2499_CONV_TIME_50_60_2X_MS },
+	[LTC2499_REJECT_50]	= { LTC2499_CONV_TIME_50_1X_MS,
+				    LTC2499_CONV_TIME_50_2X_MS },
+	[LTC2499_REJECT_60]	= { LTC2499_CONV_TIME_60_1X_MS,
+				    LTC2499_CONV_TIME_60_2X_MS },
 };
 
 static unsigned int ltc2497core_conv_time_ms(struct ltc2497core_driverdata *ddata,
@@ -42,13 +50,14 @@ static unsigned int ltc2497core_conv_time_ms(struct ltc2497core_driverdata *ddat
 {
 	/*
 	 * SPD is ignored by the part during a temperature measurement: it
-	 * always converts at 1x, so budget the 1x time regardless of the
+	 * always converts at 1x, but the rejection selection still applies, so
+	 * budget the 1x cell of the current rejection row regardless of the
 	 * selected voltage-channel mode.
 	 */
 	if (address == LTC2497_TEMP_ADDR)
-		return ltc2497core_conv_time_ms_tbl[0];
+		return ltc2497core_conv_time_ms_tbl[ddata->rejection][0];
 
-	return ltc2497core_conv_time_ms_tbl[ddata->speed_2x];
+	return ltc2497core_conv_time_ms_tbl[ddata->rejection][ddata->speed_2x];
 }
 
 static int ltc2497core_wait_conv(struct ltc2497core_driverdata *ddata,
@@ -192,11 +201,11 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev,
 		/*
 		 * Only advertised on the voltage channels of parts with a speed
 		 * mode; the sampling frequency is a property of the selected 1x/2x
-		 * mode, not of an individual conversion.
+		 * mode and rejection mode, not of an individual conversion.
 		 */
 		mutex_lock(&ddata->lock);
-		*val = ltc2497core_samp_freq_avail[ddata->speed_2x * 2];
-		*val2 = ltc2497core_samp_freq_avail[ddata->speed_2x * 2 + 1];
+		*val = ltc2497core_samp_freq_avail[ddata->rejection][ddata->speed_2x * 2];
+		*val2 = ltc2497core_samp_freq_avail[ddata->rejection][ddata->speed_2x * 2 + 1];
 		mutex_unlock(&ddata->lock);
 
 		return IIO_VAL_INT_PLUS_MICRO;
@@ -211,13 +220,17 @@ static int ltc2497core_read_avail(struct iio_dev *indio_dev,
 				  const int **vals, int *type, int *length,
 				  long mask)
 {
+	struct ltc2497core_driverdata *ddata = iio_priv(indio_dev);
+
 	switch (mask) {
-	case IIO_CHAN_INFO_SAMP_FREQ:
-		*vals = ltc2497core_samp_freq_avail;
+	case IIO_CHAN_INFO_SAMP_FREQ: {
+		guard(mutex)(&ddata->lock);
+
+		*vals = ltc2497core_samp_freq_avail[ddata->rejection];
 		*type = IIO_VAL_INT_PLUS_MICRO;
-		*length = ARRAY_SIZE(ltc2497core_samp_freq_avail);
+		*length = ARRAY_SIZE(ltc2497core_samp_freq_avail[0]);
 		return IIO_AVAIL_LIST;
-
+	}
 	default:
 		return -EINVAL;
 	}
@@ -228,24 +241,26 @@ static int ltc2497core_write_raw(struct iio_dev *indio_dev,
 				 int val, int val2, long mask)
 {
 	struct ltc2497core_driverdata *ddata = iio_priv(indio_dev);
+	const int *avail;
 	unsigned int i;
-	bool speed_2x;
 
 	switch (mask) {
-	case IIO_CHAN_INFO_SAMP_FREQ:
-		/* Match the (val, val2) pair against the advertised rates. */
-		for (i = 0; i < ARRAY_SIZE(ltc2497core_samp_freq_avail); i += 2) {
-			if (val == ltc2497core_samp_freq_avail[i] &&
-			    val2 == ltc2497core_samp_freq_avail[i + 1])
+	case IIO_CHAN_INFO_SAMP_FREQ: {
+		guard(mutex)(&ddata->lock);
+
+		/*
+		 * Match the (val, val2) pair against the rates advertised for
+		 * the rejection mode currently selected.
+		 */
+		avail = ltc2497core_samp_freq_avail[ddata->rejection];
+		for (i = 0; i < ARRAY_SIZE(ltc2497core_samp_freq_avail[0]); i += 2) {
+			if (val == avail[i] && val2 == avail[i + 1])
 				break;
 		}
-		if (i == ARRAY_SIZE(ltc2497core_samp_freq_avail))
+		if (i == ARRAY_SIZE(ltc2497core_samp_freq_avail[0]))
 			return -EINVAL;
 
-		speed_2x = i / 2;
-
-		mutex_lock(&ddata->lock);
-		ddata->speed_2x = speed_2x;
+		ddata->speed_2x = i / 2;
 		/*
 		 * The new speed only takes effect once the second command byte
 		 * is reprogrammed, so force the next read to reprogram rather
@@ -259,15 +274,73 @@ static int ltc2497core_write_raw(struct iio_dev *indio_dev,
 		 * untouched here.
 		 */
 		ddata->addr_prev = LTC2497_CONFIG_DEFAULT;
-		mutex_unlock(&ddata->lock);
 
 		return 0;
-
+	}
 	default:
 		return -EINVAL;
 	}
 }
 
+static const char * const ltc2497core_filter_modes_str[] = {
+	[LTC2499_REJECT_50_60]	= "50_60",
+	[LTC2499_REJECT_50]	= "50",
+	[LTC2499_REJECT_60]	= "60",
+};
+
+static int ltc2497core_set_filter_mode(struct iio_dev *indio_dev,
+				       const struct iio_chan_spec *chan,
+				       unsigned int val)
+{
+	struct ltc2497core_driverdata *ddata = iio_priv(indio_dev);
+
+	guard(mutex)(&ddata->lock);
+
+	ddata->rejection = val;
+	/*
+	 * The new rejection mode only takes effect once the second command byte
+	 * is reprogrammed, so force the next read to reprogram rather than reuse
+	 * the value already latched for this address.  LTC2497_CONFIG_DEFAULT is
+	 * not a valid channel/temperature address, so it is a safe re-arm
+	 * sentinel (as used at probe).
+	 *
+	 * A conversion started under the old rejection mode may still be in
+	 * flight; its own duration (conv_time_prev), not the new mode's, still
+	 * gates the next reprogram, so the timing state is left untouched here.
+	 */
+	ddata->addr_prev = LTC2497_CONFIG_DEFAULT;
+
+	return 0;
+}
+
+static int ltc2497core_get_filter_mode(struct iio_dev *indio_dev,
+				       const struct iio_chan_spec *chan)
+{
+	struct ltc2497core_driverdata *ddata = iio_priv(indio_dev);
+
+	guard(mutex)(&ddata->lock);
+
+	return ddata->rejection;
+}
+
+static const struct iio_enum ltc2497core_filter_mode_enum = {
+	.items = ltc2497core_filter_modes_str,
+	.num_items = ARRAY_SIZE(ltc2497core_filter_modes_str),
+	.set = ltc2497core_set_filter_mode,
+	.get = ltc2497core_get_filter_mode,
+};
+
+/*
+ * Rejection applies to voltage and temperature alike, so the attribute is
+ * device-wide.
+ */
+static const struct iio_chan_spec_ext_info ltc2497core_ext_info[] = {
+	IIO_ENUM("filter_mode", IIO_SHARED_BY_ALL, &ltc2497core_filter_mode_enum),
+	IIO_ENUM_AVAILABLE("filter_mode", IIO_SHARED_BY_ALL,
+			   &ltc2497core_filter_mode_enum),
+	{ }
+};
+
 #define LTC2497_CHAN(_chan, _addr, _ds_name, _extra_mask) { \
 	.type = IIO_VOLTAGE, \
 	.indexed = 1, \
@@ -380,6 +453,21 @@ int ltc2497core_probe(struct device *dev, struct iio_dev *indio_dev)
 	else
 		indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel) - 1;
 
+	if (ddata->chip_info->has_rejection_mode) {
+		struct iio_chan_spec *channels;
+
+		channels = devm_kmemdup(dev, indio_dev->channels,
+					indio_dev->num_channels * sizeof(*channels),
+					GFP_KERNEL);
+		if (!channels)
+			return -ENOMEM;
+
+		for (unsigned int i = 0; i < indio_dev->num_channels; i++)
+			channels[i].ext_info = ltc2497core_ext_info;
+
+		indio_dev->channels = channels;
+	}
+
 	ret = ddata->result_and_measure(ddata, LTC2497_CONFIG_DEFAULT, NULL);
 	if (ret < 0)
 		return ret;
@@ -404,8 +492,11 @@ int ltc2497core_probe(struct device *dev, struct iio_dev *indio_dev)
 
 	ddata->addr_prev = LTC2497_CONFIG_DEFAULT;
 	ddata->time_prev = ktime_get();
-	/* Power-on default mode is 1x; a conversion is already in flight. */
-	ddata->conv_time_prev = LTC2497_CONV_TIME_1X_MS;
+	/*
+	 * Power-on default is simultaneous 50/60Hz rejection at 1x; a conversion
+	 * is already in flight.
+	 */
+	ddata->conv_time_prev = LTC2497_CONV_TIME_50_60_1X_MS;
 
 	mutex_init(&ddata->lock);
 
diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
index 15458d4e21a1..4cccd3b7c8ef 100644
--- a/drivers/iio/adc/ltc2497.c
+++ b/drivers/iio/adc/ltc2497.c
@@ -7,6 +7,7 @@
  * Datasheet: http://cds.linear.com/docs/en/datasheet/2497fd.pdf
  */
 
+#include <linux/bitfield.h>
 #include <linux/i2c.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/driver.h>
@@ -85,32 +86,34 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
 	}
 
 	/*
-	 * Parts with a second config byte (LTC2499: internal PTAT sensor and/or
-	 * the 2x speed mode) latch their converter configuration from that byte
-	 * and only re-evaluate it when EN2 is set; a single byte, or a second
-	 * byte with EN2 = 0, means "keep previous".  A one-byte channel select
-	 * therefore cannot pull the device back out of temperature mode, so a
-	 * voltage read after a temperature read would keep returning the PTAT
-	 * result.  Always drive the second byte with EN2 set on these parts:
+	 * Parts with a second config byte (LTC2499: internal PTAT sensor, the 2x
+	 * speed mode and/or the line-rejection selection) latch their converter
+	 * configuration from that byte and only re-evaluate it when EN2 is set;
+	 * a single byte, or a second byte with EN2 = 0, means "keep previous".
+	 * A one-byte channel select therefore cannot pull the device back out of
+	 * temperature mode, so a voltage read after a temperature read would
+	 * keep returning the PTAT result.  Always drive the second byte with EN2
+	 * set on these parts:
 	 *   - temperature read: IM = 1 (SPD is ignored by the part in
-	 *     temperature mode and is left 0 here);
-	 *   - voltage read: IM = 0 (external input), plus SPD when 2x is
-	 *     selected.
-	 * FA = FB = 0 keeps the power-on simultaneous 50/60Hz rejection, whose
-	 * worst-case conversion time the driver's wait already covers.
+	 *     temperature mode and is left 0 here), plus the rejection select,
+	 *     which the part does honour while measuring temperature;
+	 *   - voltage read: IM = 0 (external input), plus the rejection select,
+	 *     plus SPD when 2x is selected.
 	 *
 	 * The byte could be skipped while the latched configuration is already
 	 * the one wanted; it is sent on every conversion for simplicity.
 	 */
-	if (ddata->chip_info->has_temp || ddata->chip_info->has_speed_mode) {
+	if (ddata->chip_info->has_temp || ddata->chip_info->has_speed_mode ||
+	    ddata->chip_info->has_rejection_mode) {
+		u8 reject = FIELD_PREP(LTC2499_REJECT, ddata->rejection);
 		u8 cmd[2];
 
 		if (address == LTC2497_TEMP_ADDR) {
 			cmd[0] = LTC2497_ENABLE | LTC2497_CONFIG_DEFAULT;
-			cmd[1] = LTC2499_EN2 | LTC2499_IM;
+			cmd[1] = LTC2499_EN2 | LTC2499_IM | reject;
 		} else {
 			cmd[0] = LTC2497_ENABLE | address;
-			cmd[1] = LTC2499_EN2;
+			cmd[1] = LTC2499_EN2 | reject;
 			if (ddata->speed_2x)
 				cmd[1] |= LTC2499_SPD;
 		}
@@ -179,6 +182,7 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
 		.name = "ltc2499",
 		.has_temp = true,
 		.has_speed_mode = true,
+		.has_rejection_mode = true,
 	},
 };
 
diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
index cee9a2f50b82..3a3fd82b21a3 100644
--- a/drivers/iio/adc/ltc2497.h
+++ b/drivers/iio/adc/ltc2497.h
@@ -4,15 +4,21 @@
 #define LTC2497_CONFIG_DEFAULT		LTC2497_ENABLE
 
 /*
- * Conversion-time bounds used to gate reads.  Each value is the datasheet
- * t_CONV maximum, rounded UP to the next whole millisecond.
+ * Conversion-time bounds used to gate reads, one per rejection/speed
+ * combination.  Each value is the datasheet t_CONV maximum, rounded UP to the
+ * next whole millisecond.
  *
  * The 2x mode (LTC2499_SPD, LTC2499 only) disables the offset auto-calibration
  * to roughly double the output rate; adding the 2x wait time is what makes the
- * SPD control actually faster.
+ * SPD control actually faster.  The simultaneous 50/60Hz 1x value is the
+ * power-up default and the only one the LTC2496/LTC2497 can be in.
  */
-#define LTC2497_CONV_TIME_1X_MS		150ULL	/* ceil(t_CONV_1 simult. max 149.9) */
-#define LTC2499_CONV_TIME_2X_MS		76ULL	/* ceil(t_CONV_2 simult. max  75.1) */
+#define LTC2497_CONV_TIME_50_60_1X_MS	150ULL	/* t_CONV_1 simult. max 149.9 */
+#define LTC2499_CONV_TIME_50_60_2X_MS	76ULL	/* t_CONV_2 simult. max  75.1 */
+#define LTC2499_CONV_TIME_50_1X_MS	164ULL	/* t_CONV_1 50Hz    max 163.5 */
+#define LTC2499_CONV_TIME_50_2X_MS	82ULL	/* t_CONV_2 50Hz    max  81.9 */
+#define LTC2499_CONV_TIME_60_1X_MS	137ULL	/* t_CONV_1 60Hz    max 136.3 */
+#define LTC2499_CONV_TIME_60_2X_MS	69ULL	/* t_CONV_2 60Hz    max  68.2 */
 
 /*
  * Sentinel passed as `address` to result_and_measure() to request a
@@ -24,13 +30,26 @@
 /* Second config-byte bits (LTC2499 / LTC2493 only) */
 #define LTC2499_EN2			BIT(7)	/* enable second config byte */
 #define LTC2499_IM			BIT(6)	/* 1 = measure internal temp sensor */
+#define LTC2499_REJECT			GENMASK(5, 4)	/* line-rejection select (FA/FB) */
 #define LTC2499_SPD			BIT(3)	/* 1 = 2x output rate (offset cal off) */
 
+/*
+ * Values of the FA/FB line-rejection field.  Rejection is honoured during a
+ * temperature conversion too, unlike SPD, which the part ignores while
+ * measuring temperature.
+ */
+enum ltc2497_rejection {
+	LTC2499_REJECT_50_60,	/* simultaneous 50/60Hz, the power-on default */
+	LTC2499_REJECT_50,
+	LTC2499_REJECT_60,
+};
+
 struct ltc2497_chip_info {
 	const char *name;
 	u32 resolution;
 	bool has_temp;
 	bool has_speed_mode;	/* SPD bit in the 2nd config byte (LTC2499/LTC2493) */
+	bool has_rejection_mode;	/* FA/FB bits in the 2nd config byte */
 };
 
 struct ltc2497core_driverdata {
@@ -41,6 +60,7 @@ struct ltc2497core_driverdata {
 	const struct ltc2497_chip_info	*chip_info;
 	u8 addr_prev;
 	bool speed_2x;	/* SPD: false = 1x (default), true = 2x */
+	enum ltc2497_rejection rejection;	/* FA/FB line-rejection select */
 	/* Conversion time (ms) of the conversion currently in flight. */
 	unsigned int conv_time_prev;
 	int (*result_and_measure)(struct ltc2497core_driverdata *ddata,

-- 
2.43.0

[PATCH v3 3/4] iio: adc: ltc2497: select the channel set per device

[Andrei Stancovici via B4 Relay]

From: Andrei Stancovici <andrei.stancovici@analog.com>

Ahead of adding a part with a different channel map, describe each
layout as a channel set in the core and let chip_info point at the one
its part uses. Probe takes the channel array and its length from there
instead of picking a table and trimming the count itself.

No functional change.

Signed-off-by: Andrei Stancovici <andrei.stancovici@analog.com>

---
Changes in v3:
- New patch. The channel-set mechanism is introduced before the LTC2493
  so that the patch adding the part does not change the chip_info of the
  parts already supported (Nuno Sá).
- chip_info references a channel set directly rather than carrying the
  single-ended input count for the core to match against a keyed table.
  That removes the probe-time search and its -EINVAL path. The count had
  no remaining user once the search was gone, so it is removed with it;
  the direct reference is what now carries the relationship the integer
  added in v2 was standing in for (Jonathan Cameron, Nuno Sá).
- pahole, struct ltc2497_chip_info, before -> after: LP64 16 -> 24
  bytes, ILP32 12 -> 16 bytes, no holes either way. The driver holds
  four of these, all static and const. The ILP32 figures were taken
  from a standalone build of the struct by the host compiler; no 32-bit
  kernel toolchain was available here.
- Verified as no functional change on hardware: the complete sysfs
  attribute tree of the LTC2497 and the LTC2499, names and values, is
  identical across this patch, and both parts still pass their full
  suites at this commit (LTC2499 36/36, LTC2497 24/24).
---
 drivers/iio/adc/ltc2496.c      |  1 +
 drivers/iio/adc/ltc2497-core.c | 27 ++++++++++++++++++---------
 drivers/iio/adc/ltc2497.c      |  2 ++
 drivers/iio/adc/ltc2497.h      | 13 +++++++++++++
 4 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/drivers/iio/adc/ltc2496.c b/drivers/iio/adc/ltc2496.c
index 5b5b6ab28850..ffddd6368755 100644
--- a/drivers/iio/adc/ltc2496.c
+++ b/drivers/iio/adc/ltc2496.c
@@ -89,6 +89,7 @@ static void ltc2496_remove(struct spi_device *spi)
 static const struct ltc2497_chip_info ltc2496_info = {
 	.resolution = 16,
 	.name = NULL,
+	.channel_set = &ltc2497_chanset_ltc2497,
 };
 
 static const struct of_device_id ltc2496_of_match[] = {
diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c
index c218d87d3a62..576a7c0a0f9b 100644
--- a/drivers/iio/adc/ltc2497-core.c
+++ b/drivers/iio/adc/ltc2497-core.c
@@ -420,6 +420,22 @@ static const struct iio_chan_spec _name[] = {                           \
 LTC2497_DEFINE_CHANNELS(ltc2497core_channel, 0);
 LTC2497_DEFINE_CHANNELS(ltc2497core_channel_samp_freq, BIT(IIO_CHAN_INFO_SAMP_FREQ));
 
+/*
+ * The temperature channel is the last entry of each table, so a part without
+ * the sensor stops one short of it.
+ */
+const struct ltc2497_channel_set ltc2497_chanset_ltc2497 = {
+	.channels	= ltc2497core_channel,
+	.num_channels	= ARRAY_SIZE(ltc2497core_channel) - 1,
+};
+EXPORT_SYMBOL_NS_GPL(ltc2497_chanset_ltc2497, "LTC2497");
+
+const struct ltc2497_channel_set ltc2497_chanset_ltc2499 = {
+	.channels	= ltc2497core_channel_samp_freq,
+	.num_channels	= ARRAY_SIZE(ltc2497core_channel_samp_freq),
+};
+EXPORT_SYMBOL_NS_GPL(ltc2497_chanset_ltc2499, "LTC2497");
+
 static const struct iio_info ltc2497core_info = {
 	.read_raw = ltc2497core_read_raw,
 	.read_avail = ltc2497core_read_avail,
@@ -443,15 +459,8 @@ int ltc2497core_probe(struct device *dev, struct iio_dev *indio_dev)
 
 	indio_dev->info = &ltc2497core_info;
 	indio_dev->modes = INDIO_DIRECT_MODE;
-	if (ddata->chip_info->has_speed_mode)
-		indio_dev->channels = ltc2497core_channel_samp_freq;
-	else
-		indio_dev->channels = ltc2497core_channel;
-	/* Only the ltc2499 has a temperature channel; it is the last entry. */
-	if (ddata->chip_info->has_temp)
-		indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel);
-	else
-		indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel) - 1;
+	indio_dev->channels = ddata->chip_info->channel_set->channels;
+	indio_dev->num_channels = ddata->chip_info->channel_set->num_channels;
 
 	if (ddata->chip_info->has_rejection_mode) {
 		struct iio_chan_spec *channels;
diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
index 4cccd3b7c8ef..984f15eb06f6 100644
--- a/drivers/iio/adc/ltc2497.c
+++ b/drivers/iio/adc/ltc2497.c
@@ -176,10 +176,12 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
 	[TYPE_LTC2497] = {
 		.resolution = 16,
 		.name = NULL,
+		.channel_set = &ltc2497_chanset_ltc2497,
 	},
 	[TYPE_LTC2499] = {
 		.resolution = 24,
 		.name = "ltc2499",
+		.channel_set = &ltc2497_chanset_ltc2499,
 		.has_temp = true,
 		.has_speed_mode = true,
 		.has_rejection_mode = true,
diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
index 3a3fd82b21a3..7335c6c0af84 100644
--- a/drivers/iio/adc/ltc2497.h
+++ b/drivers/iio/adc/ltc2497.h
@@ -44,8 +44,21 @@ enum ltc2497_rejection {
 	LTC2499_REJECT_60,
 };
 
+/*
+ * The set of channels a part exposes.  Each supported channel layout has one
+ * of these in the core; a part names its own through chip_info.
+ */
+struct ltc2497_channel_set {
+	const struct iio_chan_spec	*channels;
+	unsigned int			num_channels;
+};
+
+extern const struct ltc2497_channel_set ltc2497_chanset_ltc2497;
+extern const struct ltc2497_channel_set ltc2497_chanset_ltc2499;
+
 struct ltc2497_chip_info {
 	const char *name;
+	const struct ltc2497_channel_set *channel_set;
 	u32 resolution;
 	bool has_temp;
 	bool has_speed_mode;	/* SPD bit in the 2nd config byte (LTC2499/LTC2493) */

-- 
2.43.0

[PATCH v3 4/4] iio: adc: ltc2497: add LTC2493 support

[Andrei Stancovici via B4 Relay]

From: Andrei Stancovici <andrei.stancovici@analog.com>

The LTC2493 is the 4-channel member of the LTC2499 family: 4 single-ended
inputs or 2 differential pairs, 24-bit result, and the same command
format, internal PTAT temperature sensor, 2x speed mode and line-frequency
rejection as the LTC2499.

Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/2493fe.pdf
Signed-off-by: Andrei Stancovici <andrei.stancovici@analog.com>

---
Changes in v3:
- The channel-set mechanism moved to the preceding patch, so this one
  adds only the LTC2493: its channel table and channel set, its
  chip_info entry, and the I2C and OF identifiers. No chip_info entry of
  an already supported part is touched (Nuno Sá).
- The LTC2493 channel table is defined once, for the speed-mode layout
  the part actually uses; v2 also generated a second variant that
  nothing selected.
- Revalidated on hardware with the full series applied: LTC2493 41/41,
  LTC2499 36/36, LTC2497 24/24.
---
 drivers/iio/adc/ltc2497-core.c | 20 ++++++++++++++++++++
 drivers/iio/adc/ltc2497.c      | 11 +++++++++++
 drivers/iio/adc/ltc2497.h      |  1 +
 3 files changed, 32 insertions(+)

diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c
index 576a7c0a0f9b..6659f848256c 100644
--- a/drivers/iio/adc/ltc2497-core.c
+++ b/drivers/iio/adc/ltc2497-core.c
@@ -420,6 +420,20 @@ static const struct iio_chan_spec _name[] = {                           \
 LTC2497_DEFINE_CHANNELS(ltc2497core_channel, 0);
 LTC2497_DEFINE_CHANNELS(ltc2497core_channel_samp_freq, BIT(IIO_CHAN_INFO_SAMP_FREQ));
 
+static const struct iio_chan_spec ltc2493_channel[] = {
+	LTC2497_CHAN(0, LTC2497_SGL, "CH0", BIT(IIO_CHAN_INFO_SAMP_FREQ)),
+	LTC2497_CHAN(1, LTC2497_SGL, "CH1", BIT(IIO_CHAN_INFO_SAMP_FREQ)),
+	LTC2497_CHAN(2, LTC2497_SGL, "CH2", BIT(IIO_CHAN_INFO_SAMP_FREQ)),
+	LTC2497_CHAN(3, LTC2497_SGL, "CH3", BIT(IIO_CHAN_INFO_SAMP_FREQ)),
+	LTC2497_CHAN_DIFF(0, LTC2497_DIFF, BIT(IIO_CHAN_INFO_SAMP_FREQ)),
+	LTC2497_CHAN_DIFF(1, LTC2497_DIFF, BIT(IIO_CHAN_INFO_SAMP_FREQ)),
+	LTC2497_CHAN_DIFF(0, LTC2497_DIFF | LTC2497_SIGN,
+			  BIT(IIO_CHAN_INFO_SAMP_FREQ)),
+	LTC2497_CHAN_DIFF(1, LTC2497_DIFF | LTC2497_SIGN,
+			  BIT(IIO_CHAN_INFO_SAMP_FREQ)),
+	LTC2497_TEMP_CHANNEL,
+};
+
 /*
  * The temperature channel is the last entry of each table, so a part without
  * the sensor stops one short of it.
@@ -436,6 +450,12 @@ const struct ltc2497_channel_set ltc2497_chanset_ltc2499 = {
 };
 EXPORT_SYMBOL_NS_GPL(ltc2497_chanset_ltc2499, "LTC2497");
 
+const struct ltc2497_channel_set ltc2497_chanset_ltc2493 = {
+	.channels	= ltc2493_channel,
+	.num_channels	= ARRAY_SIZE(ltc2493_channel),
+};
+EXPORT_SYMBOL_NS_GPL(ltc2497_chanset_ltc2493, "LTC2497");
+
 static const struct iio_info ltc2497core_info = {
 	.read_raw = ltc2497core_read_raw,
 	.read_avail = ltc2497core_read_avail,
diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
index 984f15eb06f6..3bbb6d91d41c 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_LTC2493,
 	TYPE_LTC2497,
 	TYPE_LTC2499,
 };
@@ -173,6 +174,14 @@ static void ltc2497_remove(struct i2c_client *client)
 }
 
 static const struct ltc2497_chip_info ltc2497_info[] = {
+	[TYPE_LTC2493] = {
+		.resolution = 24,
+		.name = "ltc2493",
+		.channel_set = &ltc2497_chanset_ltc2493,
+		.has_temp = true,
+		.has_speed_mode = true,
+		.has_rejection_mode = true,
+	},
 	[TYPE_LTC2497] = {
 		.resolution = 16,
 		.name = NULL,
@@ -189,6 +198,7 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
 };
 
 static const struct i2c_device_id ltc2497_id[] = {
+	{ .name = "ltc2493", .driver_data = (kernel_ulong_t)&ltc2497_info[TYPE_LTC2493] },
 	{ .name = "ltc2497", .driver_data = (kernel_ulong_t)&ltc2497_info[TYPE_LTC2497] },
 	{ .name = "ltc2499", .driver_data = (kernel_ulong_t)&ltc2497_info[TYPE_LTC2499] },
 	{ }
@@ -196,6 +206,7 @@ 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,ltc2493", .data = &ltc2497_info[TYPE_LTC2493] },
 	{ .compatible = "lltc,ltc2497", .data = &ltc2497_info[TYPE_LTC2497] },
 	{ .compatible = "lltc,ltc2499", .data = &ltc2497_info[TYPE_LTC2499] },
 	{ }
diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
index 7335c6c0af84..8de35df74f28 100644
--- a/drivers/iio/adc/ltc2497.h
+++ b/drivers/iio/adc/ltc2497.h
@@ -55,6 +55,7 @@ struct ltc2497_channel_set {
 
 extern const struct ltc2497_channel_set ltc2497_chanset_ltc2497;
 extern const struct ltc2497_channel_set ltc2497_chanset_ltc2499;
+extern const struct ltc2497_channel_set ltc2497_chanset_ltc2493;
 
 struct ltc2497_chip_info {
 	const char *name;

-- 
2.43.0

Re: [PATCH v3 0/4] iio: adc: ltc2497: add LTC2493 support and line-frequency rejection

[Jonathan Cameron]

On Thu, 29 Oct 2026 00:24:25 +0200
Andrei Stancovici via B4 Relay <devnull+andrei.stancovici.analog.com@kernel.org> wrote:

> This series adds LTC2493 support to the ltc2497 driver, and adds FA/FB
> line-frequency rejection for the LTC2499 and the LTC2493.
> 
> It includes:
> - the LTC2493 device-tree binding,
> - FA/FB line-frequency rejection (50Hz, 60Hz, or both) exposed via
>   filter_mode, implemented in the core and enabled for the LTC2499,
> - a preparatory refactor giving each supported channel layout a channel
>   set in the core, referenced directly from chip_info,
> - LTC2493 support in the driver: 4 single-ended inputs or 2 differential
>   pairs, 24-bit result, same command format as the LTC2499, the internal
>   PTAT temperature channel, the 2x conversion speed mode exposed via
>   sampling_frequency, and the same rejection selection.
> 
> The rejection patch also adjusts the conversion wait time for each
> rejection mode. The 50Hz-only mode takes up to 163.5 ms at 1x, while the
> previous fixed 150 ms delay only covered the default 50/60Hz mode.
> 
> Validated on a Raspberry Pi 4 running 7.3.0-rc4, over an IIO network
> backend, with a DC1010A-A board (LTC2493), a DC1012A-A board (LTC2499)
> and an LTC2497:
> - LTC2493: 41/41 hardware tests passed,
> - LTC2499: 36/36 hardware tests passed,
> - LTC2497: 24/24 hardware tests passed,
> - all LTC2493 rejection x speed combinations were exercised without
>   conversion or I2C errors.
> 
> LTC2496 was build-tested only because no LTC2496 hardware was available.
> 
> The source in this series matches the hardware-tested tree.
> 
> Signed-off-by: Andrei Stancovici <andrei.stancovici@analog.com>
I've somewhat speculatively picked this up on basis it looks fine to me.
However, there is still time for additional review from Nuno or others
as, whilst I'll be rebasing shortly on rc1, I probably won't push out as not
rebasing until second half of the week.

So applied to the testing branch of iio.git

Thanks,

Jonathan


> ---
> Changes in v3:
> - The channel-set selection moved into a preparatory patch, so the patch
>   adding the LTC2493 no longer touches the chip_info of the parts
>   already supported (Nuno Sá).
> - chip_info now references a per-device channel set directly. The
>   num_inputs field and the keyed lookup it was matched against in probe
>   are both gone (Nuno Sá).
> - The LTC2493 patch is reduced to the device-specific additions.
> - The binding and FA/FB patches are unchanged. Nuno Sá's Reviewed-by is
>   added to the FA/FB patch.
> - Behaviour revalidated on hardware on all three parts; see the
>   validation summary above.
> - Per-patch changelogs are under the --- of each patch.
> - Link to v2: https://patch.msgid.link/20261022-submission-ltc2493-support-v1-v2-0-391d908d2877@analog.com
> 
> ---
> Andrei Stancovici (4):
>       dt-bindings: iio: adc: lltc,ltc2497: add LTC2493 support
>       iio: adc: ltc2497: add FA/FB line-frequency rejection selection
>       iio: adc: ltc2497: select the channel set per device
>       iio: adc: ltc2497: add LTC2493 support
> 
>  .../devicetree/bindings/iio/adc/lltc,ltc2497.yaml  |   7 +
>  drivers/iio/adc/ltc2496.c                          |   1 +
>  drivers/iio/adc/ltc2497-core.c                     | 208 ++++++++++++++++-----
>  drivers/iio/adc/ltc2497.c                          |  47 +++--
>  drivers/iio/adc/ltc2497.h                          |  44 ++++-
>  5 files changed, 243 insertions(+), 64 deletions(-)
> ---
> base-commit: a3b3580713f3ac5a32dc2874ee546828977a1d68
> change-id: 20261009-submission-ltc2493-support-v1-86449ede432d
> 
> Best regards,
> --  
> Andrei Stancovici <andrei.stancovici@analog.com>
> 
>