From: Alexandre Belloni <alexandre.belloni@free-electrons.com>
To: Marek Vasut <marex@denx.de>
Cc: "Stefan Wahren" <stefan.wahren@i2se.com>,
"Lars-Peter Clausen" <lars@metafoo.de>,
linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org,
"Janusz Użycki" <j.uzycki@elpromaelectronics.com>,
"Jonathan Cameron" <jic23@kernel.org>
Subject: Re: [PATCH] iio: mxs-lradc: Fix temperature offset
Date: Wed, 7 Oct 2015 02:44:47 +0200 [thread overview]
Message-ID: <20151007004447.GC3485@piout.net> (raw)
In-Reply-To: <561456ED.5010108@denx.de>
Hi,
On 07/10/2015 at 01:19:09 +0200, Marek Vasut wrote :
> >>/* The calculated value from the ADC is in Kelvin, we
> >>* want Celsius for hwmon so the offset is
> >>- * -272.15 * scale
> >>+ * -273.15 * scale
> >>*/
> >>- *val = -1075;
> >>- *val2 = 691699;
> >>+ *val = -1079;
> >>+ *val2 = 644268;
> >>
> >
> >i think it would be nice to break down the calculation of these magic values in
> >a second patch.
>
> Indeed, I agree. I hope Alexandre can send another patch for that soon :-)
>
On my side, I'm not sure this is worth more than a comment. If
necessary, I can write that the datasheet specifies that the scale is
4/1.012 here also.
Else you end up with something like that (naive implementation):
#define SCALE (4 * 1000 / 1012)
val = -273150000 * SCALE / 1000000;
val2 = 273150000 * SCALE + 1000000 * val;
I don't feel this is any clearer because we can't use floating points in
the kernel anyway.
--
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
next prev parent reply other threads:[~2015-10-07 0:45 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-06 14:22 [PATCH] iio: mxs-lradc: Fix temperature offset Alexandre Belloni
2015-10-06 18:43 ` Stefan Wahren
2015-10-06 23:19 ` Marek Vasut
2015-10-07 0:44 ` Alexandre Belloni [this message]
2015-10-07 7:12 ` Stefan Wahren
2015-10-08 21:12 ` Marek Vasut
2015-10-06 23:13 ` Marek Vasut
2015-10-11 14:03 ` Jonathan Cameron
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