From: Pavel Machek <pavel@ucw.cz>
To: NeilBrown <neilb@suse.com>
Cc: Mark Brown <broonie@kernel.org>,
Baolin Wang <baolin.wang@linaro.org>,
Felipe Balbi <balbi@kernel.org>,
Greg KH <gregkh@linuxfoundation.org>,
Sebastian Reichel <sre@kernel.org>,
Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>,
David Woodhouse <dwmw2@infradead.org>,
robh@kernel.org, Jun Li <jun.li@nxp.com>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Ruslan Bilovol <ruslan.bilovol@gmail.com>,
Peter Chen <peter.chen@freescale.com>,
Alan Stern <stern@rowland.harvard.edu>,
r.baldyga@samsung.com, grygorii.strashko@ti.com,
Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
Lee Jones <lee.jones@linaro.org>,
Charles Keepax <ckeepax@opensource.wolfsonmicro.com>,
patches@opensource.wolfsonmicro.com,
Linux PM list <linux-pm@vger.kernel.org>,
USB <linux-usb@vger.kernel.org>,
device-mainlining@lists.linuxfoundation.org,
LKML <linux-kernel@vger.kernel.org>,
"Bird, Timothy" <Tim.Bird@am.sony.com>
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 [thread overview]
Message-ID: <20160915103352.GC13132@amd> (raw)
In-Reply-To: <877fag1b6r.fsf@notabene.neil.brown.name>
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
prev parent reply other threads:[~2016-09-15 10:34 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-01 7:09 [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation Baolin Wang
2016-08-01 7:09 ` [PATCH v16 1/4] usb: gadget: Introduce the usb charger framework Baolin Wang
2016-08-01 7:09 ` [PATCH v16 2/4] usb: gadget: Support for " Baolin Wang
2016-08-01 7:09 ` [PATCH v16 3/4] usb: gadget: Integrate with the usb gadget supporting for usb charger Baolin Wang
2016-08-01 7:09 ` [PATCH v16 4/4] power: wm831x_power: Support USB charger current limit management Baolin Wang
2016-08-11 3:14 ` [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation Baolin Wang
2016-08-29 9:02 ` Baolin Wang
2016-09-06 5:40 ` NeilBrown
2016-09-06 7:40 ` Felipe Balbi
2016-09-08 6:55 ` Baolin Wang
2016-09-08 7:31 ` NeilBrown
2016-09-08 8:12 ` Baolin Wang
2016-09-08 23:13 ` NeilBrown
2016-09-09 6:46 ` Baolin Wang
2016-09-09 21:19 ` NeilBrown
2016-09-18 9:39 ` Baolin Wang
2016-10-05 7:26 ` Baolin Wang
2016-10-05 7:47 ` Felipe Balbi
2016-10-05 7:57 ` Baolin Wang
2016-10-05 10:44 ` NeilBrown
2016-10-08 3:18 ` Baolin Wang
2016-09-09 11:07 ` Mark Brown
2016-09-09 21:57 ` NeilBrown
2016-09-12 12:25 ` Mark Brown
2016-09-12 13:27 ` NeilBrown
2016-09-12 15:26 ` Mark Brown
2016-09-13 8:00 ` NeilBrown
2016-09-14 11:16 ` Mark Brown
2016-09-14 14:11 ` NeilBrown
2016-09-14 14:57 ` Mark Brown
2016-09-14 17:50 ` NeilBrown
2016-09-14 18:02 ` Mark Brown
2016-09-15 10:33 ` Pavel Machek [this message]
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