linux-kernel - Re: [PATCH 2/2] iio: adc: ltc2309: add support for ltc2305

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Message-ID: <1a257edd-2179-4653-be22-10e44681bb60@baylibre.com>
Date: Tue, 23 Dec 2025 12:38:55 -0600
From: David Lechner <dlechner@...libre.com>
To: Kyle Hsieh <kylehsieh1995@...il.com>, Lars-Peter Clausen
 <lars@...afoo.de>, Michael Hennerich <Michael.Hennerich@...log.com>,
 Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Liam Beguin <liambeguin@...il.com>
Cc: linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: adc: ltc2309: add support for ltc2305

On 12/23/25 3:12 AM, 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.
> 
> Signed-off-by: Kyle Hsieh <kylehsieh1995@...il.com>
> ---
>  drivers/iio/adc/ltc2309.c | 50 +++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 46 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/adc/ltc2309.c b/drivers/iio/adc/ltc2309.c
> index 5f0d947d0615..7a611ddd00d2 100644
> --- a/drivers/iio/adc/ltc2309.c
> +++ b/drivers/iio/adc/ltc2309.c
> @@ -1,9 +1,11 @@
>  // SPDX-License-Identifier: GPL-2.0
>  /*
>   * The LTC2309 is an 8-Channel, 12-Bit SAR ADC with an I2C Interface.
> + * The LTC2305 is a  2-Channel, 12-Bit SAR ADC with an I2C Interface.

Would be more conventional to list things in low to high order like in the
dt-bindings. (same applies throughout this patch)

>   *
>   * Datasheet:
>   * https://www.analog.com/media/en/technical-documentation/data-sheets/2309fd.pdf
> + * https://www.analog.com/media/en/technical-documentation/data-sheets/23015fb.pdf
>   *
>   * Copyright (c) 2023, Liam Beguin <liambeguin@...il.com>
>   */
> @@ -60,6 +62,13 @@ enum ltc2309_channels {
>  	LTC2309_CH7,
>  };
>  
> +enum ltc2305_channels {
> +	LTC2305_CH0_CH1 = 0,

Initializer is not strictly needed. I guess it is consistent with the
existing code though, so OK.

> +	LTC2305_CH1_CH0,
> +	LTC2305_CH0,
> +	LTC2305_CH1,
> +};
> +
>  #define LTC2309_CHAN(_chan, _addr) {				\
>  	.type = IIO_VOLTAGE,					\
>  	.indexed = 1,						\
> @@ -99,6 +108,31 @@ static const struct iio_chan_spec ltc2309_channels[] = {
>  	LTC2309_DIFF_CHAN(7, 6, LTC2309_CH7_CH6),
>  };
>  
> +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),
> +};
> +
> +struct ltc230x_chip_info {

We avoid putting "x" in names like this because the pattern breaks too often.
Just use the main driver prefix of ltc2309.

> +	const char *name;
> +	const struct iio_chan_spec *channels;
> +	int num_channels;
> +};
> +
> +static const struct ltc230x_chip_info ltc2309_chip_info = {
> +	.name = "ltc2309",
> +	.channels = ltc2309_channels,
> +	.num_channels = ARRAY_SIZE(ltc2309_channels),
> +};
> +
> +static const struct ltc230x_chip_info ltc2305_chip_info = {
> +	.name = "ltc2305",
> +	.channels = ltc2305_channels,
> +	.num_channels = ARRAY_SIZE(ltc2305_channels),
> +};
> +
>  static int ltc2309_read_raw_channel(struct ltc2309 *ltc2309,
>  				    unsigned long address, int *val)
>  {
> @@ -158,6 +192,8 @@ static const struct iio_info ltc2309_info = {
>  
>  static int ltc2309_probe(struct i2c_client *client)
>  {
> +	const struct of_device_id *match;

Unused?

> +	const struct ltc230x_chip_info *chip_info;
>  	struct iio_dev *indio_dev;
>  	struct ltc2309 *ltc2309;
>  	int ret;
> @@ -167,13 +203,17 @@ static int ltc2309_probe(struct i2c_client *client)
>  		return -ENOMEM;
>  
>  	ltc2309 = iio_priv(indio_dev);
> +	chip_info = device_get_match_data(&client->dev);

Why not i2c_get_match_data()?

> +	if (!chip_info)
> +		return -EINVAL;
> +
>  	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 +229,15 @@ static int ltc2309_probe(struct i2c_client *client)
>  }
>  
>  static const struct of_device_id ltc2309_of_match[] = {
> -	{ .compatible = "lltc,ltc2309" },
> +	{ .compatible = "lltc,ltc2309", .data = &ltc2309_chip_info },
> +	{ .compatible = "lltc,ltc2305", .data = &ltc2305_chip_info },
>  	{ }
>  };
>  MODULE_DEVICE_TABLE(of, ltc2309_of_match);
>  
>  static const struct i2c_device_id ltc2309_id[] = {
>  	{ "ltc2309" },
> +	{ "ltc2305" },

Also need to add chip_infos here.

>  	{ }
>  };
>  MODULE_DEVICE_TABLE(i2c, ltc2309_id);
>