linux-kernel - Re: [PATCH] iio: adc: ad7944: max high bits on direct read

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Message-ID: <dd7dda31525f2947060386a2b605300cf02677f2.camel@gmail.com>
Date: Wed, 07 May 2025 07:29:41 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: David Lechner <dlechner@...libre.com>, Michael Hennerich
 <Michael.Hennerich@...log.com>, Nuno Sá
 <nuno.sa@...log.com>,  Jonathan Cameron <jic23@...nel.org>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 linux-iio@...r.kernel.org,  linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: adc: ad7944: max high bits on direct read

On Mon, 2025-05-05 at 13:28 -0500, David Lechner wrote:
> Apply a mask to the raw value received over the SPI bus for unsigned
> direct reads. As we found recently, SPI controllers may not set unused
> bits to 0 when reading with bits_per_word != {8,16,32}. The ad7944 uses
> bits_per_word of 14 and 18, so we need to mask the value to be sure we
> returning the correct value to userspace during a direct read.
> 
> Fixes: d1efcf8871db ("iio: adc: ad7944: add driver for AD7944/AD7985/AD7986")
> Signed-off-by: David Lechner <dlechner@...libre.com>
> ---
> The sign_extend32() already takes care of signed reads in case that
> isn't obvious - it overwrites the unknown bits with the sign bit.
> ---

Reviewed-by: Nuno Sá <nuno.sa@...log.com>

>  drivers/iio/adc/ad7944.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/iio/adc/ad7944.c b/drivers/iio/adc/ad7944.c
> index
> 2f949fe5587318957f2e423029294ced0a6f803d..37a137bd83571b055e970a8cd483d8726972d637
> 100644
> --- a/drivers/iio/adc/ad7944.c
> +++ b/drivers/iio/adc/ad7944.c
> @@ -377,6 +377,8 @@ static int ad7944_single_conversion(struct ad7944_adc *adc,
>  
>  	if (chan->scan_type.sign == 's')
>  		*val = sign_extend32(*val, chan->scan_type.realbits - 1);
> +	else
> +		*val &= GENMASK(chan->scan_type.realbits - 1, 0);
>  
>  	return IIO_VAL_INT;
>  }
> 
> ---
> base-commit: b72f1157bfb9b92b0439e11469f7f94e47363460
> change-id: 20250505-iio-adc-ad7944-max-high-bits-on-direct-read-b358289d0337
> 
> Best regards,