From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: Re: [PATCH v3 3/6] Documentation: DT: Document twl4030-madc-battery bindings Date: Tue, 17 Mar 2015 14:59:13 +0100 Message-ID: <20150317135913.GA4034@amd> References: <1423088075-10025-1-git-send-email-marek@goldelico.com> <1423088075-10025-4-git-send-email-marek@goldelico.com> <20150316210532.GA11441@amd> <20150317084730.GA9761@amd> <940EE988-03A4-4B1B-A168-959E367953A6@goldelico.com> <20150317103746.GB3759@amd> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: "Dr. H. Nikolaus Schaller" Cc: Belisko Marek , mark.rutland@arm.com, Sebastian Reichel , Dmitry Eremin-Solenikov , David Woodhouse , Tony Lindgren , "devicetree@vger.kernel.org" , LKML , "linux-omap@vger.kernel.org" , linux-arm-kernel , Linux PM mailing list , GTA04 owners List-Id: devicetree@vger.kernel.org Hi! > >>>>> to introduce coefficients for temperature and discharge rate? > >>>> What do you mean? Nothing like that is used in current driver wh= y do > >>>> we need to add it? > >>>=20 > >>> Well, conversion between Li-ion's voltage and state of charge at = 0 > >>> current is well known: > >>=20 > >> We can=E2=80=99t measure at 0 current since the OMAP is driven fro= m battery > >> and charger and may also draw some mA=E2=80=A6 > >=20 > > Yes, but you know how many mA you are taking just now. So if you kn= ew > > the internal resistance, you could compute the voltage at 0 > > current. (And it should also work during charging, as long as you k= now > > how much current is going in.) >=20 > As far as I understand the twl4030 charger and MADC it is not possibl= e to > separate these values. It is only reporting the inflow from charger t= o > battery + system. So you don=E2=80=99t know how many mA are supplying= the system > and how many mA are left over for charging. >=20 > You can only assume how much the system is drawing while running (som= ething > between 50 and 600 mA but this depends on system activities, power st= ate > of peripherald and e.g. backlight being switched on). >=20 > I think your basic assumption that we know any time how many mA the s= ystem > is taking is not given. So.. you won't be able to get exact value while charging, but you get one while discharging, which is what really matters...? > > Yes, and that coefficient should be internal battery resistance ;-)= =2E >=20 > But where do you know this value from to write it into a DT file? > Usually you can=E2=80=99t measure it easily and for some batteries yo= u don=E2=80=99t have > a data sheet. >=20 > Contrary, the calibration curves can easily be measured on the device > (assuming that the charge level decreases/increases linearly over tim= e > between Full and Empty). If you can copy it from the data sheet, that's the easiest option. If not, you should be able to easily compute it from the charge/discharge curves or from measured voltage at different loads. Pavel --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses= /blog.html