From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from down.free-electrons.com ([37.187.137.238]:34827 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752697AbbJGApD (ORCPT ); Tue, 6 Oct 2015 20:45:03 -0400 Date: Wed, 7 Oct 2015 02:44:47 +0200 From: Alexandre Belloni To: Marek Vasut Cc: Stefan Wahren , Lars-Peter Clausen , linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, Janusz =?utf-8?Q?U=C5=BCycki?= , Jonathan Cameron Subject: Re: [PATCH] iio: mxs-lradc: Fix temperature offset Message-ID: <20151007004447.GC3485@piout.net> References: <1444141347-15301-1-git-send-email-alexandre.belloni@free-electrons.com> <415576093.114803.1444157033983.JavaMail.open-xchange@oxbaltgw07.schlund.de> <561456ED.5010108@denx.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <561456ED.5010108@denx.de> Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org 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