From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755612Ab3LURcJ (ORCPT ); Sat, 21 Dec 2013 12:32:09 -0500 Received: from zoneX.GCU-Squad.org ([194.213.125.0]:20771 "EHLO services.gcu-squad.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753252Ab3LURcH (ORCPT ); Sat, 21 Dec 2013 12:32:07 -0500 Date: Sat, 21 Dec 2013 18:30:37 +0100 From: Jean Delvare To: Guenter Roeck Cc: Anthony Olech , lm-sensors@lm-sensors.org, Anton Vorontsov , David Woodhouse , linux-kernel@vger.kernel.org, David Dajun Chen Subject: Re: [lm-sensors] [PATCH V1] fix adc to voltage calculation in da9052 power driver Message-ID: <20131221183037.2ad91f86@endymion.delvare> In-Reply-To: <20131219181049.GA6854@roeck-us.net> References: <201312181524.rBIFOv96017094@swsrvapps-02.lan> <20131218163234.714a166c@endymion.delvare> <24DF37198A1E704D9811D8F72B87EB51847ABF61@NB-EX-MBX02.diasemi.com> <20131218172402.GA18892@roeck-us.net> <24DF37198A1E704D9811D8F72B87EB51847AC2C3@NB-EX-MBX02.diasemi.com> <20131219155454.40100f4d@endymion.delvare> <20131219181049.GA6854@roeck-us.net> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-suse-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Guenter, hi Anthony, On Thu, 19 Dec 2013 10:10:49 -0800, Guenter Roeck wrote: > On Thu, Dec 19, 2013 at 03:54:54PM +0100, Jean Delvare wrote: > > BTW, you (and we) probably shouldn't waste too much energy on this. > > ADCs are only accurate to some degree anyway. If you take the > > components connected to the input into consideration, the accuracy gets > > even worse. For example, if the input voltage must be scaled down to > > fit in the ADC's range, you need at least one resistor, which in best > > cases will have a 1% accurate value (known as tolerance.) That's ten > > times the LSB of your 10-bit ADC, at which point / 1023 or / 1024 > > really makes no practical difference. Sub-percent tolerant resistors are > > expensive and rare in consumer electronics in my experience. > > True, but on the other side (and after looking into the datasheet) > the driver already calculated the voltage on adc4..6 correctly, > so unless you disagree I would like to apply the hwmon patch to -next > for consistency. The datasheet isn't the best quality I've seen. The gain values mentioned to not even match the formulas in the same cell... But I can't object to implementing conversions the way the datasheet says, no matter how suspicious. I don't really know what tree the patch is based on. Anthony said linux-next but I can't see ichg_reg_to_mA there. If volt_reg_to_mv is updated then you certainly want to update vbbat_reg_to_mv the same way, as it diverges from the datasheet just the same. Also, please update Documentation/hwmon/da9052 so that the documentation matches the actual driver code. I really would like to hear what David Dajun Chen has to say about that. He must have had a reason to use different conversions formulas than the datasheet specifies. -- Jean Delvare