Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757147AbZLNMMw (ORCPT ); Mon, 14 Dec 2009 07:12:52 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757110AbZLNMMv (ORCPT ); Mon, 14 Dec 2009 07:12:51 -0500 Received: from opensource.wolfsonmicro.com ([80.75.67.52]:37106 "EHLO opensource2.wolfsonmicro.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757080AbZLNMMu (ORCPT ); Mon, 14 Dec 2009 07:12:50 -0500 Date: Mon, 14 Dec 2009 12:12:47 +0000 From: Mark Brown To: Pavel Machek Cc: Linus Walleij , cbou@mail.ru, dwmw2@infradead.org, LKML , linux-embedded@vger.kernel.org, Brian Swetland , rpurdie@rpsys.net, lenz@cs.wisc.edu, Dirk@Opfer-Online.de, arminlitzel@web.de, Cyril Hrubis , thommycheck@gmail.com, linux-arm-kernel , dbaryshkov@gmail.com, omegamoon@gmail.com, eric.y.miao@gmail.com, utx@penguin.cz, zaurus-devel@www.linuxtogo.org Subject: Re: [POWER] battery calibration parameters from sysfs Message-ID: <20091214121247.GB22388@rakim.wolfsonmicro.main> References: <20091204104930.GA28625@sirena.org.uk> <20091207114825.GA26965@rakim.wolfsonmicro.main> <20091207165628.GA24981@rakim.wolfsonmicro.main> <20091213132413.GB1437@ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091213132413.GB1437@ucw.cz> X-Cookie: The worst is enemy of the bad. User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2152 Lines: 46 On Sun, Dec 13, 2009 at 02:24:14PM +0100, Pavel Machek wrote: > > actual charger hardware. My main concern here is that battery > > performance monitoring has no pressing need to be in kernel and that > > pushing it into the kernel creates a barrier to implementing more > > advanced schemes in userspace, which is especially serious given how > > involved this needs to be in order to be accurate. > Well, kernel provides /proc/apm emulation and many systems still rely > on it. So it would be nice to provide something halfway-decent there. Unfortunately that's really painful in kernel since you really need to do state tracking over reboots, and even if you do that it's really not trivial. > Plus you need to shutdown/suspend machine on battery critical. That > has to be in kernel and already needs those tricky parts. Power failure detection based on voltage drop is much more reasonable but it's a very different thing to general battery capacity estimation. Normally you'd want to do the power failure detection separately anyway, monitoring the system supply voltage rather than the battery voltage. Supply failure is not only an issue in battery operation, it's also an issue for example in systems systems powered over USB which may be drawing more than the 500mA that USB delivers and need to supplement the USB supply with the battery. > > I'm not sure how familiar you are with the issues surrounding trying to > > do a voltage to charge mapping for a battery but it's much more complex > > than a simple table if you want to get it accurate. There's a lot > > of > Well... current zaurus kernels use _huge_ table that maps voltage to > battery %... and that table is linear function :-(. > Do you have some papers on that? Something like "Measure Battery Capacity Precisely in Medical Design" by Bernd Krafthoefer in Power Electronics Technology Jan 2005 might be useful here. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/