linux-kernel - Re: [PATCH v9 1/4] gadget: Introduce the usb charger framework

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Message-ID: <20160406081006.GD21101@shlinux2.ap.freescale.net>
Date:	Wed, 6 Apr 2016 16:10:06 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Felipe Balbi <balbi@...nel.org>
Cc:	Baolin Wang <baolin.wang@...aro.org>, gregkh@...uxfoundation.org,
	sre@...nel.org, dbaryshkov@...il.com, dwmw2@...radead.org,
	peter.chen@...escale.com, stern@...land.harvard.edu,
	r.baldyga@...sung.com, yoshihiro.shimoda.uh@...esas.com,
	lee.jones@...aro.org, broonie@...nel.org,
	ckeepax@...nsource.wolfsonmicro.com,
	patches@...nsource.wolfsonmicro.com, linux-pm@...r.kernel.org,
	linux-usb@...r.kernel.org,
	device-mainlining@...ts.linuxfoundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 1/4] gadget: Introduce the usb charger framework

On Wed, Apr 06, 2016 at 11:05:26AM +0300, Felipe Balbi wrote:
> Peter Chen <hzpeterchen@...il.com> writes:
> > On Wed, Apr 06, 2016 at 10:38:23AM +0300, Felipe Balbi wrote:
> >> Peter Chen <hzpeterchen@...il.com> writes:
> >> > On Fri, Apr 01, 2016 at 03:21:49PM +0800, Baolin Wang wrote:
> >> >  +
> >> >> +static struct attribute *usb_charger_attrs[] = {
> >> >> +	&dev_attr_sdp_current.attr,
> >> >> +	&dev_attr_dcp_current.attr,
> >> >> +	&dev_attr_cdp_current.attr,
> >> >> +	&dev_attr_aca_current.attr,
> >> >> +	&dev_attr_charger_type.attr,
> >> >> +	&dev_attr_charger_state.attr,
> >> >> +	NULL
> >> >> +};
> >> >
> >> > The user may only care about current limit, type and state, why they
> >> > need to care what type's current limit, it is the usb charger
> >> > framework handles, the framework judge the current according to
> >> > charger type and USB state (connect/configured/suspended).
> >> 
> >> it might be useful if we want to know that $this charger doesn't really
> >> give us as much current as it advertises.
> >> 
> >
> > As my understanding, the current limit is dynamic value, it should
> > report the value the charger supports now, eg, it connects SDP, but
> > the host is suspended now, then the value should be 2mA.
> 
> yes, and that's the limit. Now consider we connect to DCP or CDP and
> limit is 2000mA but we're charging at 1000mA ;-)
> 

Does the user need to know the $this charger limit? Don't they only
care about the current charging value? I have a USB cable which can
show charging current value, it changes from time to time, when it
connects to host pc, it shows 430mA; when it connects to dedicated
charger, it shows 1000mA.

-- 

Best Regards,
Peter Chen