From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ppsw-41.csi.cam.ac.uk ([131.111.8.141]:42958 "EHLO ppsw-41.csi.cam.ac.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932826Ab1JXP6r (ORCPT ); Mon, 24 Oct 2011 11:58:47 -0400 Message-ID: <4EA58B39.8030608@cam.ac.uk> Date: Mon, 24 Oct 2011 16:58:49 +0100 From: Jonathan Cameron MIME-Version: 1.0 To: guenter.roeck@ericsson.com CC: "linux-kernel@vger.kernel.org" , "linux-iio@vger.kernel.org" , "linus.ml.walleij@gmail.com" , "zdevai@gmail.com" , "linux@arm.linux.org.uk" , "arnd@arndb.de" , "broonie@opensource.wolfsonmicro.com" , "gregkh@suse.de" , "lm-sensors@lm-sensors.org" , "khali@linux-fr.org" , "thomas.petazzoni@free-electrons.com" , "maxime.ripard@free-electrons.com" Subject: Re: [PATCH 5/6] IIO:hwmon interface client driver. References: <1319103187-27791-1-git-send-email-jic23@cam.ac.uk> <1319103187-27791-6-git-send-email-jic23@cam.ac.uk> <1319123566.3720.297.camel@groeck-laptop> <4EA03E8D.1010303@cam.ac.uk> <4EA53973.9080102@cam.ac.uk> <1319470784.2583.46.camel@groeck-laptop> In-Reply-To: <1319470784.2583.46.camel@groeck-laptop> Content-Type: text/plain; charset=UTF-8 Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org On 10/24/11 16:39, Guenter Roeck wrote: > On Mon, 2011-10-24 at 06:09 -0400, Jonathan Cameron wrote: > [ ... ] >>>>> +/* >>>>> + * Assumes that IIO and hwmon operate in the same base units. >>>>> + * This is supposed to be true, but needs verification for >>>>> + * new channel types. >>>>> + */ >>>>> +static ssize_t iio_hwmon_read_val(struct device *dev, >>>>> + struct device_attribute *attr, >>>>> + char *buf) >>>>> +{ >>>>> + long result; >>>>> + int val, ret, scaleint, scalepart; >>>>> + struct sensor_device_attribute *sattr = to_sensor_dev_attr(attr); >>>>> + struct iio_hwmon_state *state = dev_get_drvdata(dev); >>>>> + >>>>> + /* >>>>> + * No locking between this pair, so theoretically possible >>>>> + * the scale has changed. >>>>> + */ >>>>> + ret = iio_read_channel_raw(state->channels[sattr->index], >>>>> + &val); >>>>> + if (ret < 0) >>>>> + return ret; >>>>> + >>>>> + ret = iio_read_channel_scale(state->channels[sattr->index], >>>>> + &scaleint, &scalepart); >>>>> + if (ret < 0) >>>>> + return ret; >>>>> + switch (ret) { >>>>> + case IIO_VAL_INT: >>>>> + result = val * scaleint; >>>>> + break; >>>>> + case IIO_VAL_INT_PLUS_MICRO: >>>>> + result = (long)val * (long)scaleint + >>>>> + (long)val * (long)scalepart / 1000000L; >>>>> + break; >>>>> + case IIO_VAL_INT_PLUS_NANO: >>>>> + result = (long)val * (long)scaleint + >>>>> + (long)val * (long)scalepart / 1000000000L; >>>>> + break; >>>> >>>> Still easy to imagine that val * scalepart gets larger than 2147483647L >>>> (on machines where sizeof(long) = 4) ... it will already happen if the >>>> result of (val * scalepart / 1000000000) is larger than 2. >>> Good point. I really ought to have done the calcs. >>> If we have maximum possible value in here things will be ugly. >>> >>> Worst case is scalepart is 9999999999. (could be done as 1 - 0.000000001 >>> which would be nicer, but we don't specify a preference - from this >>> discussion I am suspecting we should!) >>> >>> Looks like 64 bits is going to be a requirement as you say. >>>> >>>> What value range do you expect to see here ? >>>> >>>> If (val * scaleint) is already the milli-unit, scalepart would possibly >>>> only address fractions of milli-units. If so, the result of (val * >>>> scalepart / 1000000000L) might always be smaller than 1, ie 0. >>> It certainly should be. >>>> If so, for the calculation to have any value, you might be better off using >>>> DIV_ROUND_CLOSEST(val * scalepart, 1000000000L). >>> Good idea. >>>> >>>> I am a bit confused by this anyway. Since hwmon in general reports >>>> milli-units, VAL_INT appears to reflect milli-units, VAL_INT_PLUS_MICRO >>>> really means nano-units, and IIO_VAL_INT_PLUS_NANO really means >>>> pico-units. Is this correct ? >>> Micro units of the scale factor. >>> >>> Take my test part a max1363... >>> Scale is actually 0.5 so each adc count (e.g. raw value) is 0.5millivolts. >>> >>> scale int here is 0, >>> scale part is 500,000 (so 0.5) and it returns IIO_VAL_INT_PLUS_MICRO. >> >> How about the following? It'll be extremely costly, but this isn't exactly >> a fast path! >> >> case IIO_VAL_INT_PLUS_MICRO: >> result = (s64)val * (s64)scaleint + >> div_s64((s64)val * (s64)scalepart, 1000000LL); >> break; >> case IIO_VAL_INT_PLUS_NANO: >> result = (s64)val * (s64)scaleint + >> div_s64((s64)val * (s64)scalepart, 1000000000LL); >> break; > > Is div_s64 really necessary, or would > > result = (long)val * (long)scaleint + > DIV_ROUND_CLOSEST((s64)val * (s64)scalepart, > 1000000000LL); > > work as well ? Not if you want it to compile on arm v5 by the look of it. ERROR: "__aeabi_ldivmod" [drivers/staging/iio/iio_hwmon.ko] undefined!