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

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Message-Id: <1579014948.3.0@crapouillou.net>
Date:   Tue, 14 Jan 2020 12:15:48 -0300
From:   Paul Cercueil <paul@...pouillou.net>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>
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 Chunfeng,

Le jeu., janv. 9, 2020 at 10:27, Chunfeng Yun 
<chunfeng.yun@...iatek.com> a écrit :
> 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?

Correct.

> 
>> 
>>  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?

I guess not. Would you prefer it to be disabled by default? If so, what 
would be the way to have it enabled? A flag in devicetree?

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

Yes, that would work too. The problem would be a host-only 
gpio-b-connector.

-Paul