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Subject: Re: [PATCH] iio: temperature: mcp9600: Fix temperature reading for
 negative values
From: Andrew Hepp <andrew.hepp@ahepp.dev>
In-Reply-To: <20240428144606.5b3d9a7e@jic23-huawei>
Date: Sun, 28 Apr 2024 14:46:39 -0400
Cc: Dimitri Fedrau <dima.fedrau@gmail.com>,
 Marcelo Schmitt <marcelo.schmitt1@gmail.com>,
 Lars-Peter Clausen <lars@metafoo.de>,
 linux-iio@vger.kernel.org,
 linux-kernel@vger.kernel.org
Content-Transfer-Encoding: quoted-printable
Message-Id: <C96CEE0A-920C-4BDD-9689-058B2E6D4B29@ahepp.dev>
References: <20240424185913.1177127-1-dima.fedrau@gmail.com>
 <Ziy8DsMCeAGK79E7@debian-BULLSEYE-live-builder-AMD64>
 <20240427195758.GA3350@debian> <20240428144606.5b3d9a7e@jic23-huawei>
To: Jonathan Cameron <jic23@kernel.org>

Hi all,

On Apr 28, 2024, at 9:46=E2=80=AFAM, Jonathan Cameron <jic23@kernel.org> =
wrote:

> Agreed - by my reading the original patch is correct. Maybe it would =
act
> as cleaner 'documentation' to have the sign_extend32() for the cold =
junction be
> from bit 12 rather than 15, but I'm not sure it's worth the effort.
>=20
> Andrew, would be great if you can review this fix in case we are all =
missing
> something!

I also agree that Dimitri=E2=80=99s original patch appears correct per =
the data sheet.

I think of the cold junction register as a 16 bit 2s complement signed =
integer,=20
despite the limited range. I like sign extending it from bit 15 rather =
than from 12.

I applied Dimitri=E2=80=99s patch and stuck a dev board in my icebox.

Before patch:
    # cat /sys/bus/iio/devices/iio:device0/in_temp_raw=20
    65222
    # cat /sys/bus/iio/devices/iio:device0/in_temp_ambient_raw
    65256

After patch:
    # cat /sys/bus/iio/devices/iio:device0/in_temp_raw
    -260
    # cat /sys/bus/iio/devices/iio:device0/in_temp_ambient_raw
    -212

Looks good to me! Thanks for the patch Dimitri, and thanks to all for =
the review!

Andrew=