linux-kernel - Re: [PATCH v8 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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Date:	Thu, 31 Mar 2016 11:15:05 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Baolin Wang <baolin.wang@...aro.org>, Jun Li <jun.li@....com>
Cc:	Peter Chen <hzpeterchen@...il.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Peter Chen <peter.chen@...escale.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"r.baldyga\@samsung.com" <r.baldyga@...sung.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\@opensource.wolfsonmicro.com" 
	<patches@...nsource.wolfsonmicro.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	USB <linux-usb@...r.kernel.org>,
	"device-mainlining\@lists.linuxfoundation.org" 
	<device-mainlining@...ts.linuxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 0/4] Introduce usb charger framework to deal with the usb gadget power negotation


Hi Baolin,

Baolin Wang <baolin.wang@...aro.org> writes:
>>> >> Make sense. In our company's solution, charger detection can be done
>>> >> by hardware from PMIC at first, then it will not affect the DP/DM
>>> >> line when gadget starts to enumeration.
>>> >
>>> > I see, charger type detection is done automatically by PMIC when VBUS
>>> > is detected in your case, you just assume the process is complete
>>> > before SW do gadget connect. To make the framework common, you may do
>>> one time charger type check when vbus is on, and save it to avoid repeat
>>> charger type check.
>>>
>>> OK. I'll add one judgement to check if the charger type is set in
>>> 'usb_charger_detect_type()' function.
>>
>> Just adding a judgement isn't enough here, your framework should make sure
>> usb_charger_detect_type() is called before gadget connect, with that, the
>> existing caller place just gets the charger type from the saved value.
>> The real charger type detection done by usb_charger_detect_type() can
>> be called only when vbus is on.
>> e.g. maybe in usb_udc_vbus_handler() before usb_udc_connect_control().
>
> Yeah, Like Felipe suggested, I think we need to introduce one
> 'charger_detect()' method to do the SW charger type detection at the
> right gadget state. Thanks for your comments.

Just to be clear, we add ->charger_detect() when we know of a platform
which needs to manually detect the charger type. Until then, we ignore
that situation. It might be a good idea, however, do document this in
comments on your structure definition stating that if we need to detect
charger type, a new method should be added ;-)

cheers

-- 
balbi

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