From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation Date: Thu, 15 Sep 2016 12:33:52 +0200 Message-ID: <20160915103352.GC13132@amd> References: <878tv297a0.fsf@notabene.neil.brown.name> <87y4326l44.fsf@notabene.neil.brown.name> <20160909110727.GI27946@sirena.org.uk> <87pooc7n3t.fsf@notabene.neil.brown.name> <20160912122549.GZ27946@sirena.org.uk> <87inu11c5l.fsf@notabene.neil.brown.name> <20160912152627.GA27946@sirena.org.uk> <877fag1b6r.fsf@notabene.neil.brown.name> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <877fag1b6r.fsf@notabene.neil.brown.name> Sender: linux-kernel-owner@vger.kernel.org To: NeilBrown Cc: Mark Brown , Baolin Wang , Felipe Balbi , Greg KH , Sebastian Reichel , Dmitry Eremin-Solenikov , David Woodhouse , robh@kernel.org, Jun Li , Marek Szyprowski , Ruslan Bilovol , Peter Chen , Alan Stern , r.baldyga@samsung.com, grygorii.strashko@ti.com, Yoshihiro Shimoda , Lee Jones , Charles Keepax , patches@opensource.wolfsonmicro.com, Linux PM list USB List-Id: linux-pm@vger.kernel.org Hi! > > That's not actually 100% clear to me - for what the wm831x is doing it > > probably *does* want the higher limit. This is a system inflow limit > > (as it should be for this), at least the charger will adapt to voltage > > variations though other users in the system are much less likely to do > > so. > > Interesting ... I hadn't considered that possibility. > > As long as the current remains below the maximum, the charger will > reduce the voltage towards 2V as load increases. Somewhere before it > gets there, the system will not be able to make use of the power as the > voltage will be too low to be usable. So that will naturally limit the > current being drawn. > > Not having very much electrical engineering background, I cannot say for > sure what will happen, but it seems likely that once the voltage drops > much below 4.75V, the charger won't be operating at peak efficiency, > which would be a waste. > I can easily imagine that the hardware would switch off at some voltage > level, rather than just making do with what is there. > So I'm skeptical of this approach, but I'm open to being corrected by > someone more knowledgeable than I. Devices I seen charge down to ~4.2V. This is useful thing to play with: dx.com: 406496 1" USB Current & Voltage Detector Tester Meter w/ Red LED Display - Blue Best regards, Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html