linux-kernel - Re: [PATCH v12 1/4] gadget: Introduce the usb charger framework

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Message-ID: <871t3qmw9j.fsf@linux.intel.com>
Date:	Tue, 21 Jun 2016 17:50:16 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Baolin Wang <baolin.wang@...aro.org>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>, robh@...nel.org,
	Jun Li <jun.li@....com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Ruslan Bilovol <ruslan.bilovol@...il.com>,
	Peter Chen <peter.chen@...escale.com>,
	Alan Stern <stern@...land.harvard.edu>, r.baldyga@...sung.com,
	grygorii.strashko@...com,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Lee Jones <lee.jones@...aro.org>,
	Mark Brown <broonie@...nel.org>,
	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
	patches@...nsource.wolfsonmicro.com,
	Linux PM list <linux-pm@...r.kernel.org>,
	USB <linux-usb@...r.kernel.org>,
	device-mainlining@...ts.linuxfoundation.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 1/4] gadget: Introduce the usb charger framework


Hi,

Baolin Wang <baolin.wang@...aro.org> writes:
>>> This patch introduces the usb charger driver based on usb gadget that
>>> makes an enhancement to a power driver. It works well in practice but
>>> that requires a system with suitable hardware.
>>>
>>> The basic conception of the usb charger is that, when one usb charger
>>> is added or removed by reporting from the usb gadget state change or
>>> the extcon device state change, the usb charger will report to power
>>> user to set the current limitation.
>>>
>>> The usb charger will register notifiees on the usb gadget or the extcon
>>> device to get notified the usb charger state. It also supplies the
>>> notification mechanism to userspace When the usb charger state is changed.
>>>
>>> Power user will register a notifiee on the usb charger to get notified
>>> by status changes from the usb charger. It will report to power user
>>> to set the current limitation when detecting the usb charger is added
>>> or removed from extcon device state or usb gadget state.
>>>
>>> This patch doesn't yet integrate with the gadget code, so some functions
>>> which rely on the 'gadget' are not completed, that will be implemented
>>> in the following patches.
>>>
>>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>>> Reviewed-by: Li Jun <jun.li@....com>
>>> Tested-by: Li Jun <jun.li@....com>
>>> ---
>>>  drivers/usb/gadget/Kconfig       |    7 +
>>>  drivers/usb/gadget/udc/Makefile  |    1 +
>>>  drivers/usb/gadget/udc/charger.c |  770 ++++++++++++++++++++++++++++++++++++++
>>>  include/linux/usb/charger.h      |  191 ++++++++++
>>>  include/uapi/linux/usb/charger.h |   31 ++
>>>  5 files changed, 1000 insertions(+)
>>>  create mode 100644 drivers/usb/gadget/udc/charger.c
>>>  create mode 100644 include/linux/usb/charger.h
>>>  create mode 100644 include/uapi/linux/usb/charger.h
>>>
>>> diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
>>> index 2057add..89f4e9b 100644
>>> --- a/drivers/usb/gadget/Kconfig
>>> +++ b/drivers/usb/gadget/Kconfig
>>> @@ -134,6 +134,13 @@ config U_SERIAL_CONSOLE
>>>       help
>>>          It supports the serial gadget can be used as a console.
>>>
>>> +config USB_CHARGER
>>> +     bool "USB charger support"
>>
>> you didn't build test all possibilities, did you?
>>
>> I have a feeling this won't link if USB_GADGET=m. Can you test that?
>
> OK.
>
>>
>>> diff --git a/drivers/usb/gadget/udc/charger.c b/drivers/usb/gadget/udc/charger.c
>> [...]
>>> +struct class *usb_charger_class;
>>
>> We already have a UDC class, do we really, really need another class
>> here?
>
> We want to manage the usb charger devices by this class and one usb
> charger device is not equal with one usb device which managed by UDC

Can you explain this statement? If charging is done via a USB peripheral
port, why don't we have a 1:1 mapping between charger and UDC?

> class, so can we use UDC class to manage charger devices?
> By the way, you also suggested to use the 'class' things instead of
> 'bus' in previous mail.

true, I did say that. It seems clearer, however, that we don't need this
virtual device here.

>>> +subsys_initcall(usb_charger_class_init);
>>
>> this should always work as module_init(). Please make sure that's the
>> case.
>
> we should make sure the charger class has been allocated before user
> try to add a new gadget to the udc class. So it should be issued
> before 'module_init()' (many usb drivers are at module_init level).

-EPROBE_DEFER?

-- 
balbi

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