linux-kernel - Re: [PATCH v9 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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Message-ID: <20160406170131.GO1924@sirena.org.uk>
Date:	Wed, 6 Apr 2016 10:01:31 -0700
From:	Mark Brown <broonie@...nel.org>
To:	Peter Chen <hzpeterchen@...il.com>
Cc:	Baolin Wang <baolin.wang@...aro.org>,
	Felipe Balbi <balbi@...nel.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,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Lee Jones <lee.jones@...aro.org>,
	Charles Keepax <ckeepax@...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,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 0/4] Introduce usb charger framework to deal with the
 usb gadget power negotation

On Wed, Apr 06, 2016 at 09:15:26AM +0800, Peter Chen wrote:

> > > No, this comment is common one, but only for SW detection. Eg, when
> > > the PMIC tells you it is a SDP, you can't notify to charger IC about
> > > 500mA at once, you need to do it after host allows you to do it.

> > Note that this isn't just the charger device that needs to constrain
> > current consumption - it's the entire system.  You can't charge to the
> > limit for system power draw if the USB controller is supplying the main
> > system rail.

> Sorry, I can't catch up you. USB Host (SDP or CDP) supplies power for
> USB device (not only USB controller, it is the whole system), it can
> supply more power after set configuration. See 1.4.13 from BC 1.2.

You're saying we need to notify the charger.  The charger does not in
general control the overall system current draw.

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