From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752928AbaCGPhW (ORCPT ); Fri, 7 Mar 2014 10:37:22 -0500 Received: from cantor2.suse.de ([195.135.220.15]:50596 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751033AbaCGPhU (ORCPT ); Fri, 7 Mar 2014 10:37:20 -0500 Date: Fri, 7 Mar 2014 16:37:17 +0100 From: Jean Delvare To: Laszlo Papp Cc: LKML , lm-sensors@lm-sensors.org, Guenter Roeck Subject: Re: Tachometer speed returned rather than absolute fan speed? Message-ID: <20140307163717.336873f5@endymion.delvare> In-Reply-To: References: <20140307162524.6abd34be@endymion.delvare> Organization: SUSE Linux 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 On Fri, 7 Mar 2014 15:31:44 +0000, Laszlo Papp wrote: > On Fri, Mar 7, 2014 at 3:25 PM, Jean Delvare wrote: > > Hi Laszlo, > > > > On Fri, 7 Mar 2014 14:48:01 +0000, Laszlo Papp wrote: > >> In medias res, I find this interface cumbersome: > >> http://lxr.free-electrons.com/source/Documentation/hwmon/max6650#L31 > >> > >> It returns tachometer speed rather than actual fan speed when you deal > >> with the fan1_target interface. That would be way more convenient for > >> end users like me. > >> > >> Is there any reason for not returning absolute fan speed? I guess, > >> this would break the behavior now. However, that would be a really > >> useful convenient feature. Is it possible to add a new interface for > >> that? > > > > 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? > > I was just writing a patch to improve the documentation. Tachometer > value is not equal to the fan speed, and using the terms together is > confusing. It should probably read as follows: > > "absolute fan speed in RPM based on the corresponding tachometer > value" or something similar. I just did not get the meaning of two > different values together, and I think that confused me, especially > since get_fan and get_target are doing slightly different > computations, so it took me a while to figure this out from the > datasheet. > > Better wording would have definitely helped in here. Fwiw, I asked > another kernel hacker person who also got confused telling me that he > would not know without reading the source code. I think that it is an > indication to improve the documentation. There might be better > alternatives than the one I am proposing, but at least that one clears > up that for me. I agree. I think I would just go with "measured fan speed in RPM", as tachometer is quite a technical term and the user doesn't need to know. Care to send a patch? -- Jean Delvare SUSE L3 Support