linux-kernel - Re: [PATCH v3 4/4] iio: adc: ad9467: check for backend capabilities

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Message-ID: <34e97dbb610e82953657d8354c0a343a9e1fa57a.camel@gmail.com>
Date: Wed, 14 Jan 2026 12:29:06 +0000
From: Nuno Sá <noname.nuno@...il.com>
To: Tomas Melin <tomas.melin@...sala.com>, Michael Hennerich	
 <Michael.Hennerich@...log.com>, Nuno Sa <nuno.sa@...log.com>, Lars-Peter
 Clausen <lars@...afoo.de>, Jonathan Cameron <jic23@...nel.org>, David
 Lechner	 <dlechner@...libre.com>, Andy Shevchenko <andy@...nel.org>,
 Olivier Moysan	 <olivier.moysan@...s.st.com>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] iio: adc: ad9467: check for backend capabilities

On Wed, 2026-01-14 at 10:45 +0000, Tomas Melin wrote:
> Add capability checks for operation with backends that do not support
> full set of features, but are otherwise compatible with the device.
> 
> Signed-off-by: Tomas Melin <tomas.melin@...sala.com>
> ---
>  drivers/iio/adc/ad9467.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/ad9467.c b/drivers/iio/adc/ad9467.c
> index 9cfe66425d4e91e215cccc40e24a92c5e99e9b87..349779a049ad68b4c9f72abfc40154b4a3f2e095 100644
> --- a/drivers/iio/adc/ad9467.c
> +++ b/drivers/iio/adc/ad9467.c
> @@ -645,6 +645,9 @@ static int ad9467_backend_testmode_on(struct ad9467_state *st,
>  	};
>  	int ret;
>  
> +	if (!iio_backend_has_caps(st->back, IIO_BACKEND_CAP_CALIBRATION))
> +		return 0;
> +
>  	ret = iio_backend_data_format_set(st->back, chan, &data);
>  	if (ret)
>  		return ret;
> @@ -665,6 +668,9 @@ static int ad9467_backend_testmode_off(struct ad9467_state *st,
>  	};
>  	int ret;
>  
> +	if (!iio_backend_has_caps(st->back, IIO_BACKEND_CAP_CALIBRATION))
> +		return 0;
> +
>  	ret = iio_backend_chan_disable(st->back, chan);
>  	if (ret)
>  		return ret;
> @@ -807,6 +813,9 @@ static int ad9467_calibrate(struct ad9467_state *st)
>  	bool invert = false, stat;
>  	int ret;
>  
> +	if (!iio_backend_has_caps(st->back, IIO_BACKEND_CAP_CALIBRATION))
> +		return 0;
> +

As David suggested, it might make more sense to do the check from the callers. Not as
important as within the backend functions though.

>  	/* all points invalid */
>  	bitmap_fill(st->calib_map, st->calib_map_size);
>  
> @@ -1357,7 +1366,7 @@ static int ad9467_probe(struct spi_device *spi)
>  		return ret;
>  
>  	ret = devm_iio_backend_request_buffer(&spi->dev, st->back, indio_dev);
> -	if (ret)
> +	if (ret && ret != -EOPNOTSUPP)
>  		return ret;

Don't agree with the above. I would prefer to see a dedicated CAP for buffering
otherwise I would argue why not doing the same for everything? While it might
be acceptable merging IIO_BACKEND_CAP_TEST_PATTERNS and IIO_BACKEND_CAP_CALIBRATION
(given they are related to some extent), that does not apply to buffering.

- Nuno Sá