linux-kernel - Re: [PATCH] usb: common: usb-conn-gpio: Register charger

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Message-ID: <1578536872.21256.25.camel@mhfsdcap03>
Date:   Thu, 9 Jan 2020 10:27:52 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Paul Cercueil <paul@...pouillou.net>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>, <od@...c.me>,
        <linux-usb@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: common: usb-conn-gpio: Register charger

Hi Paul,

On Wed, 2020-01-08 at 14:26 -0300, Paul Cercueil wrote:
> Hi Greg,
> 
> 
> Le mer., janv. 8, 2020 at 17:53, Greg Kroah-Hartman 
> <gregkh@...uxfoundation.org> a écrit :
> > On Tue, Jan 07, 2020 at 01:29:01AM +0100, Paul Cercueil wrote:
> >>  Register a power supply charger, whose online state depends on 
> >> whether
> >>  the USB role is set to device or not.
> > 
> > That says _what_ you are doing, but I have no idea _why_ you want to 
> > do
> > this.
> > 
> > What is this going to cause to have happen?  What new userspace api is
> > going to result?  What will a user do with this?
> 
> This is useful when the USB role is the only way to know if the device 
> is charging from USB.
There is no charger IC on your platform?

> 
> The API is the standard power supply charger API, you get a 
> /sys/class/power_supply/xxx/online node which tells you the state of 
> the charger.
> 
> The sole purpose of this is to give userspace applications a way to 
> know whether or not the charger is plugged.
> 
> > Is this going to always show up, no matter if the role is not even
> > relevant for a power supply?
> 
> I guess it'd always show up, yes. In which case would the role not be 
> relevant for a power supply? 
Do you also need it if the platform don't have battery?


> Is gpio-b-connector not always used for 
> OTG connectors?
It also supports device only mode, usually uses vBus pin to
enable/disable controller

> 
> Cheers,
> -Paul
> 
> 
> > You need a lot more text here to make this mergable.
> > 
> > thanks,
> > 
> > greg k-h
> 
>