Re: [PATCH 3/6] iio: light: max44009: Report the integration time via read_avail()

[Jonathan Cameron <jic23@kernel.org>]

On Mon,  2 Nov 2026 16:46:57 +0900
Arka Mondal <arka@arkamondal.net> wrote:

> The light channel has IIO_CHAN_INFO_INT_TIME in info_mask_separate,
> so userspace reads the integration time from
> in_illuminance_integration_time. The values it accepts are listed by
> a custom attribute called illuminance_integration_time_available.
> That name lacks the in_ prefix the core puts on the attribute it
> describes, so it is registered at the device level, and userspace
> looking for in_illuminance_integration_time_available finds nothing.
> 
> Report the list through read_avail() and drop the custom attribute
> along with the string it printed. read_avail() wants the values as
> IIO_VAL_INT_PLUS_NANO pairs, while max44009_write_int_time() rounds a
> request to the nearest supported value with find_closest_descending()
> over a flat table, so the two forms stay as separate tables.
> 
> The eight values do not change. The core prints them with nine
> decimals, so the attribute now reads 0.800000000 down to 0.006250000
> instead of 0.8 down to 0.00625.
> 
> Fixes: 6aef699a7d7e ("iio: light: add driver for MAX44009")
> Signed-off-by: Arka Mondal <arka@arkamondal.net>
> ---
> 
> Notes:
>     Compile tested only; no relevant hardware available.
> 
>  drivers/iio/light/max44009.c | 48 ++++++++++++++++++++----------------
>  1 file changed, 27 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/iio/light/max44009.c b/drivers/iio/light/max44009.c
> index 82b8a806c5fa..c27f0f9ecc44 100644
> --- a/drivers/iio/light/max44009.c
> +++ b/drivers/iio/light/max44009.c
> @@ -66,15 +66,16 @@ static const u32 max44009_int_time_ns_array[] = {
>  	6250000,  /* Manual mode only */
>  };
>  
> -static const char max44009_int_time_str[] =
> -	"0.8 "
> -	"0.4 "
> -	"0.2 "
> -	"0.1 "
> -	"0.05 "
> -	"0.025 "
> -	"0.0125 "
> -	"0.00625";
> +static const int max44009_int_time_avail[] = {
> +	0, 800000000,
> +	0, 400000000,
> +	0, 200000000,
> +	0, 100000000,
> +	0, 50000000,
> +	0, 25000000,
> +	0, 12500000,
> +	0, 6250000,
Lot of zeros...

> +};
>  
>  struct max44009_data {
>  	struct i2c_client *client;
> @@ -101,6 +102,7 @@ static const struct iio_chan_spec max44009_channels[] = {
>  		.type = IIO_LIGHT,
>  		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
>  				      BIT(IIO_CHAN_INFO_INT_TIME),
> +		.info_mask_separate_available = BIT(IIO_CHAN_INFO_INT_TIME),
>  		.event_spec = max44009_event_spec,
>  		.num_event_specs = ARRAY_SIZE(max44009_event_spec),
>  	},
> @@ -284,17 +286,21 @@ static int max44009_read_raw(struct iio_dev *indio_dev,
>  	}
>  }
>  
> -static IIO_CONST_ATTR(illuminance_integration_time_available,
> -		      max44009_int_time_str);
> -
> -static struct attribute *max44009_attributes[] = {
> -	&iio_const_attr_illuminance_integration_time_available.dev_attr.attr,
> -	NULL,
> -};
> -
> -static const struct attribute_group max44009_attribute_group = {
> -	.attrs = max44009_attributes,
> -};
> +static int max44009_read_avail(struct iio_dev *indio_dev,
> +			       struct iio_chan_spec const *chan,
> +			       const int **vals, int *type, int *length,
> +			       long mask)
> +{
> +	switch (mask) {
> +	case IIO_CHAN_INFO_INT_TIME:
> +		*vals = max44009_int_time_avail;
> +		*type = IIO_VAL_INT_PLUS_NANO;

And the reason for the extra zeros is this.  Why not use PLUS_MICRO
and drop 3 of them.

> +		*length = ARRAY_SIZE(max44009_int_time_avail);
> +		return IIO_AVAIL_LIST;
> +	default:
> +		return -EINVAL;
> +	}
> +}
>  
>  static int max44009_threshold_byte_from_fraction(int integral, int fractional)
>  {
> @@ -464,7 +470,7 @@ static const struct iio_info max44009_info = {
>  	.read_event_config = max44009_read_event_config,
>  	.write_event_value = max44009_write_event_value,
>  	.write_event_config = max44009_write_event_config,
> -	.attrs = &max44009_attribute_group,
> +	.read_avail = max44009_read_avail,
>  };
>  
>  static irqreturn_t max44009_threaded_irq_handler(int irq, void *p)