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 14:35:08 +0800
From:	Baolin Wang <baolin.wang@...aro.org>
To:	Felipe Balbi <balbi@...nel.org>
Cc:	Jun Li <jun.li@....com>, 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@...sung.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@...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" 
	<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

On 31 March 2016 at 14:18, Felipe Balbi <balbi@...nel.org> wrote:
>
> Hi,
>
> Baolin Wang <baolin.wang@...aro.org> writes:
>> [ text/plain ]
>> On 30 March 2016 at 19:24, Felipe Balbi <balbi@...nel.org> wrote:
>>>>> >> >> >
>>>>> >> >> > Seems you don't want to guarantee charger type detection is done
>>>>> >> >> > before gadget connection(pullup DP), right?
>>>>> >> >> > I see you call usb_charger_detect_type() in each gadget usb
>>>>> >> >> > state
>>>>> >> >> changes.
>>>>> >> >>
>>>>> >> >> I am not sure I get your point correctly, please correct me if I
>>>>> >> >> misunderstand you.
>>>>> >> >> We need to check the charger type at every event comes from the
>>>>> >> >> usb gadget state changes or the extcon device state changes, which
>>>>> >> >> means a new charger plugin or pullup.
>>>>> >> >>
>>>>> >> >
>>>>> >> > According to usb charger spec, my understanding is you can't do
>>>>> >> > real charger detection procedure *after* gadget _connection_(pullup
>>>>> >> > DP), also I don't
>>>>> >>
>>>>> >> Why can not? Charger detection is usually from PMIC.
>>>>> >
>>>>> > Charger detection process will impact DP/DM line state, see usb
>>>>> > charger spec v1.2 for detail detection process, section 4.6.3 says:
>>>>> >
>>>>> > "A PD is allowed to *disconnect* and repeat the charger detection
>>>>> > process multiple times while attached. The PD is required to wait for
>>>>> > a time of at least TCP_VDM_EN max between disconnecting and restarting
>>>>> > the charger detection process."
>>>>> >
>>>>> > As Peter mentioned, the charger detection should happen between VBUS
>>>>> > detection and gadget pull up DP for first plug in case. So when&after
>>>>> > gadget connect (pullup DP), you should already know the charger type.
>>>>>
>>>>> 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
>>>
>>> assuming this finishes before gadget starts is a bad idea. It would've
>>> been much more robust to delay usb_gadget_connect() until we KNOW
>>> charger detection has completed.
>>
>> It is hardware action to detect the charger type quickly. It actually
>> *gets* the charger type and does not means *detect* charger type in
>> 'usb_charger_detect_type()' function. Maybe I need to change the
>> function name as 'usb_charger_get_type()'.
>
> yes.
>
>> If some udc drivers want to detect charger type in
>> 'gadget->ops->get_charger_type()' callback, they should avoid
>> impacting DP/DM line state at the right gadget state. Thanks.
>
> they shouldn't detect is get_type(), the semantics doesn't work. If, at
> some point, we have to do SW detection of the charger, then a new
> ->charger_detect() method will have to be added.

Make sense.

>
> --
> balbi



-- 
Baolin.wang
Best Regards