From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752563AbaCHXwH (ORCPT ); Sat, 8 Mar 2014 18:52:07 -0500 Received: from mail.active-venture.com ([67.228.131.205]:61743 "EHLO mail.active-venture.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751935AbaCHXuv (ORCPT ); Sat, 8 Mar 2014 18:50:51 -0500 X-Originating-IP: 108.223.40.66 Message-ID: <531BACD9.9050206@roeck-us.net> Date: Sat, 08 Mar 2014 15:50:49 -0800 From: Guenter Roeck User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: Laszlo Papp CC: LKML , lm-sensors@lm-sensors.org Subject: Re: [lm-sensors] Tachometer speed returned rather than absolute fan speed? References: <20140307162524.6abd34be@endymion.delvare> <20140307163717.336873f5@endymion.delvare> <20140307181718.GA1027@roeck-us.net> In-Reply-To: <20140307181718.GA1027@roeck-us.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/07/2014 10:17 AM, Guenter Roeck wrote: > On Fri, Mar 07, 2014 at 03:47:08PM +0000, Laszlo Papp wrote: >> On Fri, Mar 7, 2014 at 3:37 PM, Jean Delvare wrote: >>>>> I'm quite confused. While I admit that the term "tachometer speed" is >>>>> awkward, the max6650 driver is reporting fan speeds in RPM as every >>>>> other hwmon driver. So I really have no idea what you think is wrong. >>>>> What did you think "tachometer speed" was, if not the fan speed? Does >>>>> the max6650 driver not return correct fan speeds for you? >> >> That is some strange behavior. If I do "echo 1 > pwm1_enable; echo 0 > >> pwm1; cat fan1_input", I still see 30 for the connected fan, whereas I >> can see it stopped. Is this an expected behavior? I would expect zero >> as a user. >> > I seem to recall that I had seen that as well, with no fan connected. > Maybe the tachometer registers always read at least '1'. I would think > it is wrong, but we'll have to understand the chip a bit better > to be able to provide a fix. Unless you already have a fix ready, > of course. I'll try to re-test tonight if I find the time. > The reason is (most likely) that your fan input does not have a pull-up resistor. Per datasheet, the fan inputs need a 10kOhm pull-up resistor. I confirmed this with my test board - with the pull-up resistor, inputs read 0, Without pull-up, the reported value is 1, which translates to 30 RPM. You might also need the 10 uF capacitor on the FB pin. Guenter