iio: adc: Add support for LTC2378 and similar ADCs

PATCH In review Marcelo Schmitt 4 participants 7 messages Aug 13 – Aug 31

Subsystems (2)

IIO LTC2378 IIO ADC driver

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Marcelo Schmitt

author maintainer

2026-08-13 23:05 UTC #0 lore raw

v10 cover iio: adc: Add support for LTC2378 and similar ADCs

Improvementes to LTC2378 device driver according to v9 review.

Rebased on top of
54355e3b189c ("iio: adc: ltc2378: Enable triggered buffer data capture") Will require rebasing testing and togreg branches.

Change log v9 -> v10:
[DT]
No changes in device tree doc.
[IIO]
- Added {} to make local variable at top of code block scope.
- if-else code neat.
- Mention the possibility of having same index for diff channels (e.g. voltageX-voltageX) in ABI doc.

With best regards,
Marcelo

Marcelo Schmitt (2):
iio: adc: ltc2378: Add support for LTC2338-18
iio: ABI: Encourage differential voltage ABI usage

 Documentation/ABI/testing/sysfs-bus-iio | 11 ++++---
 drivers/iio/adc/ltc2378.c               | 44 +++++++++++++++++++++++--
 2 files changed, 49 insertions(+), 6 deletions(-)

base-commit: 54355e3b189c7015d4575ae04a3bc7b803975bd1

Signature · 1 line

2.53.0

Marcelo Schmitt

author maintainer

2026-08-13 23:05 UTC #1 lore raw

PATCH v10 1/2 iio: adc: ltc2378: Add support for LTC2338-18

LTC2338-18 is similar to LTC2378-18, differentiating from the already supported part mainly on the embedment of an internal voltage reference and addition of a resistor divider network connected to the input signal path. Extend the device driver, handling the internal reference and input signal attenuation, enabling it to also support LTC2338-18.

Signed-off-by Marcelo Schmitt <[email protected]>

---
Change log v9 -> v10:
- Added {} to make local variable at top of code block scope.
- if-else code neat.

 drivers/iio/adc/ltc2378.c | 44 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 42 insertions(+), 2 deletions(-)

drivers/iio/adc/ltc2378.c +42 -2

index 146eaadbeb6c..74ac6b8cb7c4 100644
@@ -107,6 +107,8 @@
 
 struct ltc2378_chip_info {
 	const char *name;
+	unsigned int internal_ref_uV;
+	struct u32_fract internal_div;
 	struct iio_chan_spec chan[2]; /* 1 physical chan + 1 timestamp chan */
 	struct iio_chan_spec offload_chan;
 	unsigned int max_sample_rate_Hz;

@@ -145,6 +147,16 @@ struct ltc2378_state {
 	} scan __aligned(IIO_DMA_MINALIGN);
 };
 
+static const struct ltc2378_chip_info ltc2338_18_chip_info = {
+	.name = "ltc2338-18",
+	.internal_ref_uV = 2048000,
+	.internal_div = { .numerator = 5, .denominator = 2 },
+	.chan = { LTC2378_DIFF_CHANNEL(18), IIO_CHAN_SOFT_TIMESTAMP(1) },
+	.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(18),
+	.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
+	.tconv_ns = 527,
+};
+
 static const struct ltc2378_chip_info ltc2364_16_chip_info = {
 	.name = "ltc2364-16",
 	.chan = { LTC2378_PSEUDO_DIFF_CHANNEL(16), IIO_CHAN_SOFT_TIMESTAMP(1) },

@@ -382,8 +394,11 @@ static int ltc2378_read_raw(struct iio_dev *indio_dev,
 
 		return IIO_VAL_INT;
 	}
-	case IIO_CHAN_INFO_SCALE:
+	case IIO_CHAN_INFO_SCALE: {
+		struct u32_fract fract = st->info->internal_div;
 		*val = st->ref_uV / MILLI;
+		if (fract.numerator && fract.denominator)
+			*val = mult_frac(*val, fract.numerator, fract.denominator);
 		/*
 		 * For all LTC2378-like devices, the amount of bits that express
 		 * voltage magnitude depend on the polarity / output code format:

@@ -396,6 +411,7 @@ static int ltc2378_read_raw(struct iio_dev *indio_dev,
 			*val2 = chan->scan_type.realbits;
 
 		return IIO_VAL_FRACTIONAL_LOG2;
+	}
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		*val = st->cnv_Hz;
 		return IIO_VAL_INT;

@@ -641,6 +657,25 @@ static const struct spi_offload_config ltc2378_offload_config = {
 			    SPI_OFFLOAD_CAP_RX_STREAM_DMA,
 };
 
+static int ltc2378_refin_setup(struct device *dev, struct ltc2378_state *st)
+{
+	int ret;
+
+	/*
+	 * The internal reference buffer amplifies both the internal reference
+	 * and REFIN by a factor of 2.
+	 */
+	ret = devm_regulator_get_enable_read_voltage(dev, "refin");
+	if (ret == -ENODEV) /* refin is optional */
+		st->ref_uV = st->info->internal_ref_uV * 2;
+	else if (ret < 0)
+		return dev_err_probe(dev, ret, "failed to read refin regulator\n");
+	else
+		st->ref_uV = ret * 2;
+
+	return 0;
+}
+
 static int ltc2378_ref_setup(struct device *dev, struct ltc2378_state *st)
 {
 	int ret;

@@ -676,7 +711,10 @@ static int ltc2378_probe(struct spi_device *spi)
 	if (!st->info)
 		return -EINVAL;
 
-	ret = ltc2378_ref_setup(dev, st);
+	if (st->info->internal_ref_uV)
+		ret = ltc2378_refin_setup(dev, st);
+	else
+		ret = ltc2378_ref_setup(dev, st);
 	if (ret)
 		return ret;

@@ -750,6 +788,7 @@ static int ltc2378_probe(struct spi_device *spi)
 }
 
 static const struct of_device_id ltc2378_of_match[] = {
+	{ .compatible = "adi,ltc2338-18", .data = &ltc2338_18_chip_info },
 	{ .compatible = "adi,ltc2364-16", .data = &ltc2364_16_chip_info },
 	{ .compatible = "adi,ltc2364-18", .data = &ltc2364_18_chip_info },
 	{ .compatible = "adi,ltc2367-16", .data = &ltc2367_16_chip_info },

@@ -774,6 +813,7 @@ static const struct of_device_id ltc2378_of_match[] = {
 MODULE_DEVICE_TABLE(of, ltc2378_of_match);
 
 static const struct spi_device_id ltc2378_spi_id[] = {
+	{ .name = "ltc2338-18", .driver_data = (kernel_ulong_t)&ltc2338_18_chip_info },
 	{ .name = "ltc2364-16", .driver_data = (kernel_ulong_t)&ltc2364_16_chip_info },
 	{ .name = "ltc2364-18", .driver_data = (kernel_ulong_t)&ltc2364_18_chip_info },
 	{ .name = "ltc2367-16", .driver_data = (kernel_ulong_t)&ltc2367_16_chip_info },

Signature · 1 line

2.53.0

Andy Shevchenko

Reviewed-by on v10 1/2

2026-08-17 07:28 UTC #2 lore raw

Re: [PATCH v10 1/2] iio: adc: ltc2378: Add support for LTC2338-18

Quoted 5 lines · Marcelo Schmitt

LTC2338-18 is similar to LTC2378-18, differentiating from the already supported part mainly on the embedment of an internal voltage reference and addition of a resistor divider network connected to the input signal path. Extend the device driver, handling the internal reference and input signal attenuation, enabling it to also support LTC2338-18.

LGTM now,

Reviewed-by Andy Shevchenko <[email protected]>

...

drivers/iio/adc/ltc2378.c static int ltc2378_read_raw(struct iio_dev *indio_dev, · line 398

Quoted 3 lines

drivers/iio/adc/ltc2378.c +2 -1

-	case IIO_CHAN_INFO_SCALE:
+	case IIO_CHAN_INFO_SCALE: {
+		struct u32_fract fract = st->info->internal_div;

+ blank line

drivers/iio/adc/ltc2378.c static int ltc2378_read_raw(struct iio_dev *indio_dev, · line 401

Quoted 3 lines

drivers/iio/adc/ltc2378.c +2 -0

 		*val = st->ref_uV / MILLI;
+		if (fract.numerator && fract.denominator)
+			*val = mult_frac(*val, fract.numerator, fract.denominator);

He-he, I have a local patch to add mult_fract() macro for this kind of cases :-) Perhaps need to submit it at some point...

Signature · 2 lines

With Best Regards,
Andy Shevchenko

Jonathan Cameron

maintainer

2026-08-22 02:20 UTC #3 lore raw

Re: [PATCH v10 1/2] iio: adc: ltc2378: Add support for LTC2338-18

Quoted 9 lines · On Mon, 17 Aug 2026 10:28:21 +0300 Andy Shevchenko…

Quoted 5 lines · Marcelo Schmitt
LTC2338-18 is similar to LTC2378-18, differentiating from the already supported part mainly on the embedment of an internal voltage reference and addition of a resistor divider network connected to the input signal path. Extend the device driver, handling the internal reference and input signal attenuation, enabling it to also support LTC2338-18.
LGTM now,
Reviewed-by Andy Shevchenko <[email protected]>

Ah. I applied the earlier version fixing up at least comments it seems. (Not that I've completely forgotten doing so!)

Can you please check if there is anything different we can handle as a follow on patch?

Thanks,

Jonathan

Quoted 16 lines

...
drivers/iio/adc/ltc2378.c static int ltc2378_read_raw(struct iio_dev *indio_dev, · line 398
Quoted 3 lines
drivers/iio/adc/ltc2378.c +2 -1
-	case IIO_CHAN_INFO_SCALE:
+	case IIO_CHAN_INFO_SCALE: {
+		struct u32_fract fract = st->info->internal_div;  
+ blank line
drivers/iio/adc/ltc2378.c static int ltc2378_read_raw(struct iio_dev *indio_dev, · line 401
Quoted 3 lines
drivers/iio/adc/ltc2378.c +2 -0
 		*val = st->ref_uV / MILLI;
+		if (fract.numerator && fract.denominator)
+			*val = mult_frac(*val, fract.numerator, fract.denominator);  
He-he, I have a local patch to add mult_fract() macro for this kind of cases :-) Perhaps need to submit it at some point...

Andy Shevchenko

2026-08-24 08:21 UTC #4 lore raw

Re: [PATCH v10 1/2] iio: adc: ltc2378: Add support for LTC2338-18

Quoted 9 lines · Jonathan Cameron

Quoted 7 lines · On Mon, 17 Aug 2026 10:28:21 +0300 Andy Shevchenko…
Quoted 5 lines · Marcelo Schmitt
LTC2338-18 is similar to LTC2378-18, differentiating from the already supported part mainly on the embedment of an internal voltage reference and addition of a resistor divider network connected to the input signal path. Extend the device driver, handling the internal reference and input signal attenuation, enabling it to also support LTC2338-18.

Quoted 7 lines

Quoted 2 lines
LGTM now,
Reviewed-by Andy Shevchenko <[email protected]>
Ah. I applied the earlier version fixing up at least comments it seems. (Not that I've completely forgotten doing so!)
Can you please check if there is anything different we can handle as a follow on patch?

Hmm... Are you asking me doing this? I would delegate this to Marcelo. If we forget something, I don't think it would be a big deal. I just have almost no time for this.

Signature · 2 lines

With Best Regards,
Andy Shevchenko

Marcelo Schmitt

2026-08-24 12:30 UTC #5 lore raw

Re: [PATCH v10 1/2] iio: adc: ltc2378: Add support for LTC2338-18

Quoted 10 lines · Andy Shevchenko

Quoted 9 lines · Jonathan Cameron
Quoted 7 lines · On Mon, 17 Aug 2026 10:28:21 +0300 Andy Shevchenko…
Quoted 5 lines · Marcelo Schmitt
LTC2338-18 is similar to LTC2378-18, differentiating from the already supported part mainly on the embedment of an internal voltage reference and addition of a resistor divider network connected to the input signal path. Extend the device driver, handling the internal reference and input signal attenuation, enabling it to also support LTC2338-18.

Quoted 8 lines

Quoted 7 lines
Quoted 2 lines
LGTM now,
Reviewed-by Andy Shevchenko <[email protected]>
Ah. I applied the earlier version fixing up at least comments it seems. (Not that I've completely forgotten doing so!)
Can you please check if there is anything different we can handle as a follow on patch?

I'll wait a week or so until the release cycle rush ends to send a follow on patch.

Quoted 4 lines

Hmm... Are you asking me doing this? I would delegate this to Marcelo. If we forget something, I don't think it would be a big deal. I just have almost no time for this.

Agree, the difference from the applied version to v10 is just condestyle/readability. No functional change or bug fix of any sort being made.

With Best Regards,
Marcelo

Jonathan Cameron

maintainer

2026-08-31 02:12 UTC #6 lore raw

Re: [PATCH v10 1/2] iio: adc: ltc2378: Add support for LTC2338-18

In reply to Andy Shevchenko

Quoted 15 lines · On Mon, 24 Aug 2026 11:21:40 +0300 Andy Shevchenko…

Quoted 14 lines · Jonathan Cameron
Quoted 9 lines · On Mon, 17 Aug 2026 10:28:21 +0300 Andy Shevchenko…
Quoted 5 lines · Marcelo Schmitt
LTC2338-18 is similar to LTC2378-18, differentiating from the already supported part mainly on the embedment of an internal voltage reference and addition of a resistor divider network connected to the input signal path. Extend the device driver, handling the internal reference and input signal attenuation, enabling it to also support LTC2338-18.
LGTM now,
Reviewed-by Andy Shevchenko <[email protected]>
Ah. I applied the earlier version fixing up at least comments it seems. (Not that I've completely forgotten doing so!)

Quoted 7 lines

Quoted 2 lines
Can you please check if there is anything different we can handle as a follow on patch?
Hmm... Are you asking me doing this? I would delegate this to Marcelo. If we forget something, I don't think it would be a big deal. I just have almost no time for this.

Indeed not! Sorry - should have been explicit that I meant Marcelo as author of the series.

Jonathan