linux-kernel - RE: [PATCH v2 3/3] power/supply: Add generic USB charger driver

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Message-Id: <1576755337.3.0@crapouillou.net>
Date:   Thu, 19 Dec 2019 12:35:37 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     Peter Chen <peter.chen@....com>
Cc:     Sebastian Reichel <sre@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>, od@...c.me,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: RE: [PATCH v2 3/3] power/supply: Add generic USB charger driver

Hi Peter,


Le mer., déc. 18, 2019 at 02:46, Peter Chen <peter.chen@....com> a 
écrit :
> 
>>  >>  >
>>  >>  >>  >>  +
>>  >>  >>  >>  +	desc = &charger->desc;
>>  >>  >>  >>  +	desc->name = "usb-charger";
>>  >>  >>  >>  +	desc->properties = usb_charger_properties;
>>  >>  >>  >>  +	desc->num_properties = 
>> ARRAY_SIZE(usb_charger_properties);
>>  >>  >>  >>  +	desc->get_property = usb_charger_get_property;
>>  >>  >>  >>  +	desc->type = POWER_SUPPLY_TYPE_USB;
>>  >>  >>  >
>>  >>  >>  > What's your further plan for this generic USB charger?
>>  >>  >>  > To support BC1.2, we need to know charger type, and how we
>>  >> could  >> get  > it?
>>  >>  >>  >
>>  >>  >>  > Peter
>>  >>  >>
>>  >>  >>  Well I don't really know. The USB role framework does not 
>> give
>>  >> any  >> info about  what's plugged.
>>  >>  >>
>>  >>  >
>>  >>  > What's the use case for this patch set? How it be used?
>>  >>
>>  >>  My devicetree:
>>  >>
>>  >>  usb_otg: usb@...40000 {
>>  >>  	compatible = "ingenic,jz4770-musb", "simple-mfd";
>>  >>  	reg = <0x13440000 0x10000>;
>>  >>  	[...]
>>  >>
>>  >>  	usb-role-switch;
>>  >>
>>  >>  	connector {
>>  >>  		compatible = "gpio-usb-b-connector", "usb-b-connector";
>>  >>  		label = "mini-USB";
>>  >>  		type = "mini";
>>  >>
>>  >>  		id-gpios = <&gpf 18 GPIO_ACTIVE_HIGH>;
>>  >>  		vbus-gpios = <&gpb 5 GPIO_ACTIVE_HIGH>;
>>  >>  		[...]
>>  >>  	};
>>  >>
>>  >>  	usb_charger: usb-charger {
>>  >>  		compatible = "usb-charger";
>>  >>  	};
>>  >>  };
>>  >>
>>  >>  The new gpio-usb-connector driver uses the ID/VBUS GPIOs to 
>> detect
>>  >> in  which state (device, host, unconnected) a OTG connector is.
>>  >> However,  that means I cannot use the standard gpio-charger 
>> driver to
>>  >> detect the  presence of a charger based on the state of the VBUS
>>  >> gpio, since it's  already requested here. So the point of this
>>  >> patchset is to provide an  alternative to gpio-charger that works
>>  >> with OTG controllers compatible  with 'usb-role-switch'.
>>  >>
>>  >
>>  > Thanks for explaining it.
>>  >
>>  > What's the user for this USB charger,  PMIC or what else? How the 
>> user
>>  > uses this USB charger interface?
>> 
>>  It's exported as a standard charger, so it can be passed to client 
>> drivers through
>>  devicetree, and its online status can be retrieved from sysfs.
>> 
> 
> Hi Paul,
> 
> If you would like to get role from usb-role-switch, the udc driver 
> may probably have already worked.
> There is a 'state' entry under the udc device to indicate USB Ch9 
> state. Try to see if it could
> satisfy your requirement.

This is not the proper way to retrieve charger status.
Linux supports chargers through the power supply subsystem, that's 
where it should be exported.

Cheers,
-Paul