linux-kernel - Re: [PATCH v7 5/5] iio: ad4080: Rework filter

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Message-ID: <0f515c35-b2ac-4d23-b8bb-77151ed2eb9f@baylibre.com>
Date: Tue, 26 Aug 2025 11:51:56 -0500
From: David Lechner <dlechner@...libre.com>
To: Ben Collins <bcollins@...nel.org>, Jonathan Cameron <jic23@...nel.org>,
 Nuno Sá <nuno.sa@...log.com>,
 Andy Shevchenko <andy@...nel.org>,
 Antoniu Miclaus <antoniu.miclaus@...log.com>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 5/5] iio: ad4080: Rework filter_type "none" logic

On 8/25/25 7:10 PM, Ben Collins wrote:
> The filter_type logic for "none" needed to be reworked to be more
> general.
> 
> As documented, return IIO_VAL_EMPTY for sampling rates in "none" type
> and EINVAL when there's an attempt to write a rate for "none" type.

This patch breaks usespace, which is something we always must avoid.

> 
> Signed-off-by: Ben Collins <bcollins@...nel.org>
> ---
>  drivers/iio/adc/ad4080.c | 23 ++++++++++-------------
>  1 file changed, 10 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad4080.c b/drivers/iio/adc/ad4080.c
> index 6e61787ed3213fe4332bd92b938a7a717dada99f..c7408b9703731ee5d4229a85ffa91ea64b233cd9 100644
> --- a/drivers/iio/adc/ad4080.c
> +++ b/drivers/iio/adc/ad4080.c
> @@ -154,8 +154,6 @@ static const int ad4080_dec_rate_avail[] = {
>  	2, 4, 8, 16, 32, 64, 128, 256, 512, 1024,
>  };
>  
> -static const int ad4080_dec_rate_none[] = { 1 };
> -
>  static const char * const ad4080_power_supplies[] = {
>  	"vdd33", "vdd11", "vddldo", "iovdd", "vrefin",
>  };
> @@ -268,13 +266,13 @@ static int ad4080_read_raw(struct iio_dev *indio_dev,
>  			*val = st->clk_rate;
>  		return IIO_VAL_INT;
>  	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> -		if (st->filter_type == FILTER_NONE) {
> -			*val = 1;
> -		} else {
> -			*val = ad4080_get_dec_rate(indio_dev, chan);
> -			if (*val < 0)
> -				return *val;
> -		}
> +		if (st->filter_type == FILTER_NONE)
> +			return IIO_VAL_EMPTY;
> +
> +		*val = ad4080_get_dec_rate(indio_dev, chan);
> +		if (*val < 0)
> +			return *val;
> +
>  		return IIO_VAL_INT;
>  	default:
>  		return -EINVAL;
> @@ -289,7 +287,7 @@ static int ad4080_write_raw(struct iio_dev *indio_dev,
>  
>  	switch (mask) {
>  	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> -		if (st->filter_type == FILTER_NONE && val > 1)
> +		if (st->filter_type == FILTER_NONE)
>  			return -EINVAL;
>  
>  		return ad4080_set_dec_rate(indio_dev, chan, val);
> @@ -376,17 +374,16 @@ static int ad4080_read_avail(struct iio_dev *indio_dev,
>  	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
>  		switch (st->filter_type) {
>  		case FILTER_NONE:
> -			*vals = ad4080_dec_rate_none;
> -			*length = ARRAY_SIZE(ad4080_dec_rate_none);
> +			*type = IIO_VAL_EMPTY;
>  			break;
>  		default:
>  			*vals = ad4080_dec_rate_avail;
>  			*length = st->filter_type >= SINC_5 ?
>  				  (ARRAY_SIZE(ad4080_dec_rate_avail) - 2) :
>  				  ARRAY_SIZE(ad4080_dec_rate_avail);
> +			*type = IIO_VAL_INT;
>  			break;
>  		}
> -		*type = IIO_VAL_INT;
>  		return IIO_AVAIL_LIST;
>  	default:
>  		return -EINVAL;
> 

Returning a value of 1 for the oversampling ratio when there is no
oversampling going on is perfectly reasonable and mathematically correct.
So I don't consider this change an improvement.