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

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Date:   Wed, 08 Jan 2020 14:26:10 -0300
From:   Paul Cercueil <paul@...pouillou.net>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Chunfeng Yun <chunfeng.yun@...iatek.com>, 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 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.

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? Is gpio-b-connector not always used for 
OTG connectors?

Cheers,
-Paul

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