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

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Date:	Wed, 22 Jun 2016 09:49:24 +0800
From:	Baolin Wang <baolin.wang@...aro.org>
To:	Felipe Balbi <balbi@...nel.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

On 21 June 2016 at 22:50, Felipe Balbi <balbi@...nel.org> wrote:
>
> 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?

Sorry for confusing, but forget it, I plan to remove the device/class
things as you suggested.

>
>> 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.

OK.

>
>>>> +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?

OK. But 'EPROBE_DEFER' is not needed if we remove the class things.

-- 
Baolin.wang
Best Regards