linux-kernel - Re: [PATCH] iio: dac: ad5592r: fix temperature scale

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Message-ID: <20240430145935.0000055d@Huawei.com>
Date: Tue, 30 Apr 2024 14:59:35 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: <marc.ferland@...il.com>
CC: <lars@...afoo.de>, <Michael.Hennerich@...log.com>, <jic23@...nel.org>,
	<linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Marc Ferland
	<marc.ferland@...atest.com>
Subject: Re: [PATCH] iio: dac: ad5592r: fix temperature scale

On Tue, 30 Apr 2024 09:13:30 -0400
marc.ferland@...il.com wrote:

> From: Marc Ferland <marc.ferland@...atest.com>
> 
> For temperature readings, the remainder is returned as nano Celsius
> _but_ we mark it as IIO_VAL_INT_PLUS_MICRO. This results in incorrect
> temperature reporting through hwmon for example. I have a board here
> which reports the following when running 'sensors':
> 
> iio_hwmon-isa-0000
> Adapter: ISA adapter
> temp1:        +93.3°C
> 
> With the patch applied, it returns the correct temperature:
> 
> iio_hwmon-isa-0000
> Adapter: ISA adapter
> temp1:        +30.5°C
> 
> Signed-off-by: Marc Ferland <marc.ferland@...atest.com>

IIO temperature units are milli celcius, so I'm not following
the argument here.  The driver might be reporting in pico celcius
I suppose?  Call out that this is the scale factor though, so
it corresponds to 1LSB hence a small number is certainly plausible..

Reasonable to argue it's taking the integer and dividing by 10^9 hence
INT_PLUS_NANO is the right answer, but it isn't nano celsius.


Jonathan


> ---
>  drivers/iio/dac/ad5592r-base.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/dac/ad5592r-base.c b/drivers/iio/dac/ad5592r-base.c
> index 076bc9ecfb49..4763402dbcd6 100644
> --- a/drivers/iio/dac/ad5592r-base.c
> +++ b/drivers/iio/dac/ad5592r-base.c
> @@ -415,7 +415,7 @@ static int ad5592r_read_raw(struct iio_dev *iio_dev,
>  			s64 tmp = *val * (3767897513LL / 25LL);
>  			*val = div_s64_rem(tmp, 1000000000LL, val2);
>  
> -			return IIO_VAL_INT_PLUS_MICRO;
> +			return IIO_VAL_INT_PLUS_NANO;
>  		}
>  
>  		mutex_lock(&st->lock);
> 
> base-commit: 98369dccd2f8e16bf4c6621053af7aa4821dcf8e