linux-kernel - Re: [PATCH v7 1/4] gadget: Introduce the usb charger framework

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Date:	Mon, 18 Apr 2016 13:23:28 +0200
From:	Pavel Machek <pavel@....cz>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Felipe Balbi <balbi@...nel.org>,
	Baolin Wang <baolin.wang@...aro.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Peter Chen <peter.chen@...escale.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"r.baldyga@...sung.com" <r.baldyga@...sung.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Lee Jones <lee.jones@...aro.org>,
	Mark Brown <broonie@...nel.org>,
	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
	"patches@...nsource.wolfsonmicro.com" 
	<patches@...nsource.wolfsonmicro.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	USB <linux-usb@...r.kernel.org>,
	"device-mainlining@...ts.linuxfoundation.org" 
	<device-mainlining@...ts.linuxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 1/4] gadget: Introduce the usb charger framework

Hi!

On Mon 2016-04-18 10:59:23, David Laight wrote:
> From: Pavel Machek
> > Sent: 18 April 2016 11:40
> ...
> > > >> > Actually, less is not stupid. Charging li-ion battery from li-ion battery might
> > > >> > be stupid. Imagine I'm on train, with device like N900 (50% battery) and power bank
> > > >> > (3Ah). I'm actively using the device. If I let it charge at full current, I'll waste
> > > >> > energy. If I limit current to approximately the power consumption, it will run the
> > > >> > powerbank empty, first, then empty the internal battery, maximizing total time I
> > > >> > can use the device.
> > > >>
> > > >> why would you waste energy ? What the charger chip would do is charge
> > > >> battery to maximum then just to maintenance charge from that point
> > > >> on. Where is energy being wasted other than normal heat dissipation ?
> > > >
> > > > Physics 101, of course wasted energy goes to heat. Lets not waste
> > > > energy by charging li-ion from li-ion when it is not required.
> > >
> > > your cellphone has no means to know that it's connected to a Li-Ion
> > > battery. We don't have visibility on what we're connected to, just how
> > > much it can source.
> > 
> > But cellphone user knows what he connected his charger to, and that's
> > why it is useful to be able to lower the current. Even when you said
> > "less is just stupid" I demonstrated it is not, at least in case when
> > your power source is a battery.
> 
> It reality you may want the phone/tablet to be configurable to take power
> from USB, but disable the li-ion charging circuit.
> That will maximise the time you get when running from an external battery.
> I connect my tablet to the 1A output (which discharges the internal battery
> slowly) rather than the 2A one (which will charge it with some
> cables).

Yes, being able to power device from external without charging the
battery is useful, too.

But I'd still like to control individual currents, too. If I have
power bank and two devices, I may want to select which one charges
faster.

Best regards,									
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html