linux-kernel - Re: [PATCH 1/2] iio: adc: ad9467: include two's complement in default mode

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Message-ID: <20251221195434.2bdde0e6@jic23-huawei>
Date: Sun, 21 Dec 2025 19:54:34 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Tomas Melin <tomas.melin@...sala.com>
Cc: Michael Hennerich <Michael.Hennerich@...log.com>, Nuno Sa
 <nuno.sa@...log.com>, Lars-Peter Clausen <lars@...afoo.de>, David Lechner
 <dlechner@...libre.com>, Andy Shevchenko <andy@...nel.org>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] iio: adc: ad9467: include two's complement in
 default mode

On Tue, 16 Dec 2025 11:40:05 +0000
Tomas Melin <tomas.melin@...sala.com> wrote:

> All supported drivers currently implicitly use two's complement mode.
> Make this clear by declaring two's complement in the default
> output mode. Calibration mode uses offset binary, so change the output
> mode only when running the calibration or other test mode.
> 
> Signed-off-by: Tomas Melin <tomas.melin@...sala.com>
A few comments inline, along with the obvious build error fix
from the bot report of including linux/bitfield.h

> ---
>  drivers/iio/adc/ad9467.c | 33 +++++++++++++++++++++++++--------
>  1 file changed, 25 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad9467.c b/drivers/iio/adc/ad9467.c
> index 59c3fa3bcc9b0b8b36b78c3b54fd7977cae23496..60fc3361b2689a4c38287c613ef93fe00338e5fa 100644
> --- a/drivers/iio/adc/ad9467.c
> +++ b/drivers/iio/adc/ad9467.c

> @@ -671,10 +678,14 @@ static int ad9467_backend_testmode_off(struct ad9467_state *st,
>  
>  static int ad9647_calibrate_prepare(struct ad9467_state *st)
>  {
> +	unsigned int cmode;
>  	unsigned int c;
>  	int ret;
>  
> -	ret = ad9467_outputmode_set(st, st->info->default_output_mode);
> +	cmode = (st->info->default_output_mode & ~AN877_ADC_OUTPUT_MODE_MASK) |
> +		FIELD_PREP(AN877_ADC_OUTPUT_MODE_MASK,
> +			   AN877_ADC_OUTPUT_MODE_OFFSET_BINARY);
As below. Maybe copy then FIELD_MODIFY() the result.

> +	ret = ad9467_outputmode_set(st, cmode);
>  	if (ret)
>  		return ret;
>  
> @@ -778,7 +789,7 @@ static int ad9647_calibrate_stop(struct ad9467_state *st)
>  			return ret;
>  	}
>  
> -	mode = st->info->default_output_mode | AN877_ADC_OUTPUT_MODE_TWOS_COMPLEMENT;
> +	mode = st->info->default_output_mode;
>  	return ad9467_outputmode_set(st, mode);
>  }
>  
> @@ -1174,12 +1185,18 @@ static ssize_t ad9467_chan_test_mode_write(struct file *file,
>  		if (ret)
>  			return ret;
>  
> -		out_mode = st->info->default_output_mode | AN877_ADC_OUTPUT_MODE_TWOS_COMPLEMENT;
> +		out_mode = st->info->default_output_mode;
>  		ret = ad9467_outputmode_set(st, out_mode);
>  		if (ret)
>  			return ret;
>  	} else {
> -		ret = ad9467_outputmode_set(st, st->info->default_output_mode);
> +		unsigned int cmode;
> +
> +		cmode = (st->info->default_output_mode &
> +			~AN877_ADC_OUTPUT_MODE_MASK) |
> +			FIELD_PREP(AN877_ADC_OUTPUT_MODE_MASK,
> +				   AN877_ADC_OUTPUT_MODE_OFFSET_BINARY);
Might be cleaner as
		unsigned int cmode = st->info->default_output_mode;

		FIELD_MODIFY(AN877_ADC_OUTPUT_MODE_MASK, &cmode, 
			     AN877_ADC_OUTPUT_MODE_OFFSET_BINARY);

I don't mind that much though if you prefer the original.

> +		ret = ad9467_outputmode_set(st, cmode);
>  		if (ret)
>  			return ret;
>  
>