Re: [PATCH 2/3] drivers: iio: adc: LTC2499 support

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 22 Aug 2022 15:51:05 +0300
Ciprian Regus <ciprian.regus@analog.com> wrote:

> The LTC2499 is a 16-channel (eight differential), 24-bit,
> ADC with Easy Drive technology and a 2-wire, I2C interface.
> 
> Implement support for the LTC2499 ADC by extending the LTC2497
> driver. A new chip_info struct is added to differentiate between
> chip types and resolutions when reading data from the device.
> 
> Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/2499fe.pdf
> 
> Signed-off-by: Ciprian Regus <ciprian.regus@analog.com>
Hi Ciprian,

Various comments inline.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/ltc2496.c      |  8 +++++++-
>  drivers/iio/adc/ltc2497-core.c |  2 +-
>  drivers/iio/adc/ltc2497.c      | 34 +++++++++++++++++++++++++++++-----
>  drivers/iio/adc/ltc2497.h      | 13 ++++++++++++-
>  4 files changed, 49 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/iio/adc/ltc2496.c b/drivers/iio/adc/ltc2496.c
> index dfb3bb5997e5..98338104c24a 100644
> --- a/drivers/iio/adc/ltc2496.c
> +++ b/drivers/iio/adc/ltc2496.c
> @@ -14,6 +14,7 @@
>  #include <linux/iio/iio.h>
>  #include <linux/iio/driver.h>
>  #include <linux/module.h>
> +#include <linux/property.h>
why?

>  #include <linux/mod_devicetable.h>
>  
>  #include "ltc2497.h"
> @@ -74,6 +75,7 @@ static int ltc2496_probe(struct spi_device *spi)
>  	spi_set_drvdata(spi, indio_dev);
>  	st->spi = spi;
>  	st->common_ddata.result_and_measure = ltc2496_result_and_measure;
> +	st->common_ddata.chip_info = device_get_match_data(dev);
>  
>  	return ltc2497core_probe(dev, indio_dev);
>  }
> @@ -85,8 +87,12 @@ static void ltc2496_remove(struct spi_device *spi)
>  	ltc2497core_remove(indio_dev);
>  }
>  
> +static struct chip_info ltc2496_info = {
> +	.resolution = 16,
> +};
> +
>  static const struct of_device_id ltc2496_of_match[] = {
> -	{ .compatible = "lltc,ltc2496", },
> +	{ .compatible = "lltc,ltc2496", .data = (void *)&ltc2496_info },

as below. Take the chip_info structure const and drop the cast.

>  	{},
>  };
>  MODULE_DEVICE_TABLE(of, ltc2496_of_match);
> diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c
> index 2a485c8a1940..b2752399402c 100644
> --- a/drivers/iio/adc/ltc2497-core.c
> +++ b/drivers/iio/adc/ltc2497-core.c
> @@ -95,7 +95,7 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev,
>  			return ret;
>  
>  		*val = ret / 1000;
> -		*val2 = 17;
> +		*val2 = ddata->chip_info->resolution + 1;
>  
>  		return IIO_VAL_FRACTIONAL_LOG2;
>  
> diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
> index f7c786f37ceb..bb5e0d4301e2 100644
> --- a/drivers/iio/adc/ltc2497.c
> +++ b/drivers/iio/adc/ltc2497.c
> @@ -7,10 +7,14 @@
>   * Datasheet: http://cds.linear.com/docs/en/datasheet/2497fd.pdf
>   */
>  
> +#include <linux/bitfield.h>
> +#include <linux/bitops.h>

Not immediately obvious why these need adding as part of this patch.
If just general include improvement, separate patch please.

> +
Why blank line?
>  #include <linux/i2c.h>
>  #include <linux/iio/iio.h>
>  #include <linux/iio/driver.h>
>  #include <linux/module.h>
> +#include <linux/property.h>

May make sense, but not obvious why it's in this patch.
If it's missing and should be present, please do it in a separate patch.

>  #include <linux/mod_devicetable.h>
>  
>  #include "ltc2497.h"
> @@ -19,6 +23,8 @@ struct ltc2497_driverdata {
>  	/* this must be the first member */
>  	struct ltc2497core_driverdata common_ddata;
>  	struct i2c_client *client;
> +	u32 recv_size;
> +	u32 sub_lsb;

>  	/*
>  	 * DMA (thus cache coherency maintenance) may require the
>  	 * transfer buffers to live in their own cache lines.
> @@ -34,13 +40,14 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
>  	int ret;
>  
>  	if (val) {
> -		ret = i2c_master_recv(st->client, (char *)&st->buf, 3);
> +		ret = i2c_master_recv(st->client, (char *)&st->buf, st->recv_size);
Not helpful yet, but there was a patch series under review form Jason Gerecke that
changed the i2c transfer commands to use a u8.  

Which raises a question. buf is a __be32 which is rather odd given size of 3 in original
code.  If we have a case where it needs to have separate types for different transfers, use
a union.

>  		if (ret < 0) {
>  			dev_err(&st->client->dev, "i2c_master_recv failed\n");
>  			return ret;
>  		}
>  
> -		*val = (be32_to_cpu(st->buf) >> 14) - (1 << 17);

Old code here is less than ideal, should be reading into 3 bytes then using
the be24 accesors. Please fix whilst here.  You will need multiple paths here
depending on size.

> +		*val = (be32_to_cpu(st->buf) >> st->sub_lsb) -
> +			BIT(ddata->chip_info->resolution + 1);
>  	}
>  
>  	ret = i2c_smbus_write_byte(st->client,
> @@ -54,6 +61,7 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
>  static int ltc2497_probe(struct i2c_client *client,
>  			 const struct i2c_device_id *id)
>  {
> +	u32 resolution;
>  	struct iio_dev *indio_dev;
>  	struct ltc2497_driverdata *st;
>  	struct device *dev = &client->dev;
> @@ -70,6 +78,11 @@ static int ltc2497_probe(struct i2c_client *client,
>  	i2c_set_clientdata(client, indio_dev);
>  	st->client = client;
>  	st->common_ddata.result_and_measure = ltc2497_result_and_measure;
> +	st->common_ddata.chip_info = device_get_match_data(dev);
> +
> +	resolution = st->common_ddata.chip_info->resolution;
> +	st->sub_lsb = 31 - (resolution + 1);
> +	st->recv_size = resolution / BITS_PER_BYTE + 1;
>  
>  	return ltc2497core_probe(dev, indio_dev);
>  }
> @@ -83,15 +96,26 @@ static int ltc2497_remove(struct i2c_client *client)
>  	return 0;
>  }
>  
> +static struct chip_info ltc2497_info[] = {

Should be const - which is why you need the cast below.

> +	[TYPE_LTC2497] = {
> +		.resolution = 16,
> +	},
> +	[TYPE_LTC2499] = {
> +		.resolution = 24,
> +	}
> +};
> +
>  static const struct i2c_device_id ltc2497_id[] = {
> -	{ "ltc2497", 0 },
> +	{ "ltc2497", TYPE_LTC2497 },
> +	{ "ltc2499", TYPE_LTC2499 },
>  	{ }
>  };
>  MODULE_DEVICE_TABLE(i2c, ltc2497_id);
>  
>  static const struct of_device_id ltc2497_of_match[] = {
> -	{ .compatible = "lltc,ltc2497", },
> -	{},
> +	{ .compatible = "lltc,ltc2497", .data = (void *)&ltc2497_info[TYPE_LTC2497] },
> +	{ .compatible = "lltc,ltc2499", .data = (void *)&ltc2497_info[TYPE_LTC2499] },
Cast is a bad sign.  Reason above.

> +	{}
>  };
>  MODULE_DEVICE_TABLE(of, ltc2497_of_match);
>  
> diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
> index d0b42dd6b8ad..f4d939cfd48b 100644
> --- a/drivers/iio/adc/ltc2497.h
> +++ b/drivers/iio/adc/ltc2497.h
> @@ -4,9 +4,20 @@
>  #define LTC2497_CONFIG_DEFAULT		LTC2497_ENABLE
>  #define LTC2497_CONVERSION_TIME_MS	150ULL
>  
> +enum chip_type {
> +	TYPE_LTC2496,
> +	TYPE_LTC2497,
> +	TYPE_LTC2499
> +};
> +
> +struct chip_info {
> +	u32 resolution;
> +};
> +
>  struct ltc2497core_driverdata {
>  	struct regulator *ref;
> -	ktime_t	time_prev;
> +	ktime_t time_prev;
I'm staring at this and can't see the difference between the two lines.
Closer inspection (i.e. messing with the stuff around it) tells me line
you are removing has a tab when should be a space.  Whilst trivial please
call that out in patch description (or do it as a separate patch).

> +	const struct chip_info *chip_info;
>  	u8 addr_prev;
>  	int (*result_and_measure)(struct ltc2497core_driverdata *ddata,
>  				  u8 address, int *val);