linux-kernel - Re: [PATCH] iio: temperature: mcp9600: Fix temperature reading for negative values

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Date: Mon, 29 Apr 2024 20:44:09 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Andrew Hepp <andrew.hepp@...pp.dev>
Cc: Dimitri Fedrau <dima.fedrau@...il.com>, Marcelo Schmitt
 <marcelo.schmitt1@...il.com>, Lars-Peter Clausen <lars@...afoo.de>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: temperature: mcp9600: Fix temperature reading for
 negative values

On Sun, 28 Apr 2024 14:46:39 -0400
Andrew Hepp <andrew.hepp@...pp.dev> wrote:

> Hi all,
> 
> On Apr 28, 2024, at 9:46 AM, Jonathan Cameron <jic23@...nel.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.
> > 
> > Andrew, would be great if you can review this fix in case we are all missing
> > something!  
> 
> I also agree that Dimitri’s original patch appears correct per the data sheet.
> 
> I think of the cold junction register as a 16 bit 2s complement signed integer, 
> despite the limited range. I like sign extending it from bit 15 rather than from 12.
> 
> I applied Dimitri’s patch and stuck a dev board in my icebox.
> 
> Before patch:
>     # cat /sys/bus/iio/devices/iio:device0/in_temp_raw 
>     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
That definitely deserves a Tested-by tag so I added one. Hope you don't mind!

Applied to the fixes-togreg branch of iio.git and marked for stable.

Thanks,

Jonathan