Add support for the 2-channel LTC2305 ADC in the existing LTC2309 driver.
The LTC2305 and LTC2309 share similar features: both are 12-bit,
low-noise, low-power SAR ADCs with an I2C interface.
The main difference is the number of channels: LTC2305 has 2 channels,
while LTC2309 has 8 channels.

Signed-off-by: Kyle Hsieh <kylehsieh1995@gmail.com>
---
 drivers/iio/adc/ltc2309.c | 49 ++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 44 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/adc/ltc2309.c b/drivers/iio/adc/ltc2309.c
index 5f0d947d0615..e6c15200a134 100644
--- a/drivers/iio/adc/ltc2309.c
+++ b/drivers/iio/adc/ltc2309.c
@@ -1,8 +1,10 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
+ * The LTC2305 is a  2-Channel, 12-Bit SAR ADC with an I2C Interface.
  * The LTC2309 is an 8-Channel, 12-Bit SAR ADC with an I2C Interface.
  *
  * Datasheet:
+ * https://www.analog.com/media/en/technical-documentation/data-sheets/23015fb.pdf
  * https://www.analog.com/media/en/technical-documentation/data-sheets/2309fd.pdf
  *
  * Copyright (c) 2023, Liam Beguin <liambeguin@gmail.com>
@@ -41,6 +43,13 @@ struct ltc2309 {
 };
 
 /* Order matches expected channel address, See datasheet Table 1. */
+enum ltc2305_channels {
+	LTC2305_CH0_CH1 = 0x0,
+	LTC2305_CH1_CH0 = 0x4,
+	LTC2305_CH0     = 0x8,
+	LTC2305_CH1     = 0xc,
+};
+
 enum ltc2309_channels {
 	LTC2309_CH0_CH1 = 0,
 	LTC2309_CH2_CH3,
@@ -80,6 +89,13 @@ enum ltc2309_channels {
 	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
 }
 
+static const struct iio_chan_spec ltc2305_channels[] = {
+	LTC2309_CHAN(0, LTC2305_CH0),
+	LTC2309_CHAN(1, LTC2305_CH1),
+	LTC2309_DIFF_CHAN(0, 1, LTC2305_CH0_CH1),
+	LTC2309_DIFF_CHAN(1, 0, LTC2305_CH1_CH0),
+};
+
 static const struct iio_chan_spec ltc2309_channels[] = {
 	LTC2309_CHAN(0, LTC2309_CH0),
 	LTC2309_CHAN(1, LTC2309_CH1),
@@ -99,6 +115,24 @@ static const struct iio_chan_spec ltc2309_channels[] = {
 	LTC2309_DIFF_CHAN(7, 6, LTC2309_CH7_CH6),
 };
 
+struct ltc2309_chip_info {
+	const char *name;
+	const struct iio_chan_spec *channels;
+	int num_channels;
+};
+
+static const struct ltc2309_chip_info ltc2305_chip_info = {
+	.name = "ltc2305",
+	.channels = ltc2305_channels,
+	.num_channels = ARRAY_SIZE(ltc2305_channels),
+};
+
+static const struct ltc2309_chip_info ltc2309_chip_info = {
+	.name = "ltc2309",
+	.channels = ltc2309_channels,
+	.num_channels = ARRAY_SIZE(ltc2309_channels),
+};
+
 static int ltc2309_read_raw_channel(struct ltc2309 *ltc2309,
 				    unsigned long address, int *val)
 {
@@ -158,6 +192,7 @@ static const struct iio_info ltc2309_info = {
 
 static int ltc2309_probe(struct i2c_client *client)
 {
+	const struct ltc2309_chip_info *chip_info;
 	struct iio_dev *indio_dev;
 	struct ltc2309 *ltc2309;
 	int ret;
@@ -167,13 +202,15 @@ static int ltc2309_probe(struct i2c_client *client)
 		return -ENOMEM;
 
 	ltc2309 = iio_priv(indio_dev);
+	chip_info = i2c_get_match_data(client);
+
 	ltc2309->dev = &indio_dev->dev;
 	ltc2309->client = client;
 
-	indio_dev->name = "ltc2309";
+	indio_dev->name = chip_info->name;
 	indio_dev->modes = INDIO_DIRECT_MODE;
-	indio_dev->channels = ltc2309_channels;
-	indio_dev->num_channels = ARRAY_SIZE(ltc2309_channels);
+	indio_dev->channels = chip_info->channels;
+	indio_dev->num_channels = chip_info->num_channels;
 	indio_dev->info = &ltc2309_info;
 
 	ret = devm_regulator_get_enable_read_voltage(&client->dev, "vref");
@@ -189,13 +226,15 @@ static int ltc2309_probe(struct i2c_client *client)
 }
 
 static const struct of_device_id ltc2309_of_match[] = {
-	{ .compatible = "lltc,ltc2309" },
+	{ .compatible = "lltc,ltc2305", .data = &ltc2305_chip_info },
+	{ .compatible = "lltc,ltc2309", .data = &ltc2309_chip_info },
 	{ }
 };
 MODULE_DEVICE_TABLE(of, ltc2309_of_match);
 
 static const struct i2c_device_id ltc2309_id[] = {
-	{ "ltc2309" },
+	{ "ltc2305", (kernel_ulong_t)&ltc2305_chip_info },
+	{ "ltc2309", (kernel_ulong_t)&ltc2309_chip_info },
 	{ }
 };
 MODULE_DEVICE_TABLE(i2c, ltc2309_id);

-- 
2.34.1

On Wed, Mar 11, 2026 at 09:43:02AM +0800, Kyle Hsieh wrote:
> Add support for the 2-channel LTC2305 ADC in the existing LTC2309 driver.
> The LTC2305 and LTC2309 share similar features: both are 12-bit,
> low-noise, low-power SAR ADCs with an I2C interface.
> The main difference is the number of channels: LTC2305 has 2 channels,
> while LTC2309 has 8 channels.

...

>  /* Order matches expected channel address, See datasheet Table 1. */

This comment now confusing, it should be kept at the initial enum, but the
better idea is...

> +enum ltc2305_channels {
> +	LTC2305_CH0_CH1 = 0x0,
> +	LTC2305_CH1_CH0 = 0x4,
> +	LTC2305_CH0     = 0x8,
> +	LTC2305_CH1     = 0xc,
> +};
> +
>  enum ltc2309_channels {
>  	LTC2309_CH0_CH1 = 0,
>  	LTC2309_CH2_CH3,

...to assign proper values (in necessary order) explicitly and adjust comment.
Then add this patch on top.

>  }

-- 
With Best Regards,
Andy Shevchenko

On Wed, Mar 11, 2026 at 3:11 PM Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
>
> On Wed, Mar 11, 2026 at 09:43:02AM +0800, Kyle Hsieh wrote:
> > Add support for the 2-channel LTC2305 ADC in the existing LTC2309 driver.
> > The LTC2305 and LTC2309 share similar features: both are 12-bit,
> > low-noise, low-power SAR ADCs with an I2C interface.
> > The main difference is the number of channels: LTC2305 has 2 channels,
> > while LTC2309 has 8 channels.
>
> ...
>
> >  /* Order matches expected channel address, See datasheet Table 1. */
>
> This comment now confusing, it should be kept at the initial enum, but the
> better idea is...
>
> > +enum ltc2305_channels {
> > +     LTC2305_CH0_CH1 = 0x0,
> > +     LTC2305_CH1_CH0 = 0x4,
> > +     LTC2305_CH0     = 0x8,
> > +     LTC2305_CH1     = 0xc,
> > +};
> > +
> >  enum ltc2309_channels {
> >       LTC2309_CH0_CH1 = 0,
> >       LTC2309_CH2_CH3,
>
> ...to assign proper values (in necessary order) explicitly and adjust comment.
> Then add this patch on top.
>

Thanks for your suggestion.
It makes sense to have explicit values for both chips to avoid
confusion with array indices.
I will split this into a series in v5:
1. A preparation patch to refactor ltc2309_channels using explicit hex
values from the datasheet.
2. The patch to add ltc2305 support on top of that.

> >  }
>
> --
> With Best Regards,
> Andy Shevchenko
>
>

Best Regards,
Kyle Hsieh