linux-kernel - Re: [PATCH v12 2/4] gadget: Support for the usb charger framework

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Date:	Wed, 29 Jun 2016 15:06:46 +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 2/4] gadget: Support for the usb charger framework


Hi,

Baolin Wang <baolin.wang@...aro.org> writes:
>>>>>>> For supporting the usb charger, it adds the usb_charger_init() and
>>>>>>> usb_charger_exit() functions for usb charger initialization and exit.
>>>>>>>
>>>>>>> It will report to the usb charger when the gadget state is changed,
>>>>>>> then the usb charger can do the power things.
>>>>>>>
>>>>>>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>>>>>>> Reviewed-by: Li Jun <jun.li@....com>
>>>>>>> Tested-by: Li Jun <jun.li@....com>
>>>>>>
>>>>>> Before anything, I must say that I really liked this patch. It's
>>>>>> minimaly invasive to udc core and does all the necessary changes. If it
>>>>>> wasn't for the extra charger class, this would've been perfect.
>>>>>>
>>>>>> Can't you just tie a charger to a UDC and avoid the charger class
>>>>>> completely?
>>>>>>
>>>>>>>  static inline int usb_gadget_vbus_draw(struct usb_gadget *gadget, unsigned mA)
>>>>>>>  {
>>>>>>> +     if (gadget->charger)
>>>>>>
>>>>>> I guess you could do this check inside
>>>>>> usb_gadget_set_cur_limit_by_type() itself.
>>>>>
>>>>> We will access the 'gadget->charger->type' member when issuing
>>>>> usb_gadget_set_cur_limit_by_type(), so I think I should leave the
>>>>> check here in next new version.
>>>>
>>>> Here's what I mean:
>>>>
>>>> int usb_charger_set_cur_limit(struct usb_gadget *gadget, unsigned int mA)
>>>> {
>>>>         struct usb_charger *charger;
>>>>         enum usb_charger_type type;
>>>>
>>>>         if (!gadget->charger)
>>>>                 return 0;
>>>>
>>>>         charger = gadget->charger;
>>>>         type = charger->type;
>>>>
>>>>         return __usb_charger_set_cur_limit(charger, type, mA);
>>>> }
>>>
>>> But that means we need to export  both 'usb_charger_set_cur_limit()'
>>> function and '__usb_charger_set_cur_limit()' function in charger.c
>>> file. Cause some user may want to set the current limitation by one
>>> charger type parameter (may be not from charger->type), like by
>>> issuing '__usb_charger_set_cur_limit(charger, SDP_TYPE, mA)'. How do
>>> you think about this situation? Thanks.
>>
>> if we have that requirement, that's totally fine. Just rename
>> __usb_charger_set_cur_limit() back to
>> _usb_charger_set_cur_limit_by_type() and expose both. But
>> set_cur_limit_by_type can assume its arguments are valid at all times.
>
> Make sense. I'll fix this issue in v14 version. Thanks.

there's one thing bothering me though:

gadget->charger is supposed to be "current detected charger" right? If
we have a single port tied to a single charger, in which case would we
*ever* need to change current limit of any charger type other than
"current charger" ?

IOW, why do we need _set_cur_limit_by_type() exported at all?

-- 
balbi

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