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

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Message-ID: <87r3bggotf.fsf@linux.intel.com>
Date:	Wed, 29 Jun 2016 15:30:20 +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" ?
>
> What I mean is user can set the current limit by charger type as what
> they want at initial stage. As we know the default current of SDP (not
> super speed) is 500 mA, but user can set the current limit of SDP as
> 450 mA if there are some special on their own platform by issuing
> '__usb_charger_set_cur_limit(charger, SDP_TYPE, 450)'.

Oh I see. Odd, but okay

-- 
balbi

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