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

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Date:	Thu, 07 Apr 2016 07:56:50 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Peter Chen <hzpeterchen@...il.com>
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


Hi,

Peter Chen <hzpeterchen@...il.com> writes:
> On Wed, Apr 06, 2016 at 01:25:06PM +0300, Felipe Balbi wrote:
>> 
>> Hi,
>> 
>> Peter Chen <hzpeterchen@...il.com> writes:
>> > 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
>> 
>> Why not ? UI might want to change the color of the battery charging icon
>> if we're charging @ 2000mA or @ 1000mA to give some visual feedback as
>> to "how fast" battery is supposed to be charged.
>> 
>> > 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.
>> 
>> good for you, now what does that have to do with $subject ?
>> 
>
> +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
> +};
>
> Ok, even the users are interesting in current limit, we still have no
> necessary to know all kinds of chargers limit and current value, since
> we already have charger type user interface, the framework can show
> limit according to charger type.

Oh, now I get your comment and I totally agree. We already *know* the
detected charger type, there's no point in showing them all.

> I think below user interfaces are enough, who do you think?
>
> +static struct attribute *usb_charger_attrs[] = {
> +	&dev_attr_current.attr,
> +	&dev_attr_current_limit.attr,
> +	&dev_attr_charger_type.attr,
> +	&dev_attr_charger_state.attr,
> +	NULL
> +};

agreed, const though.

-- 
balbi

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