RE: [PATCH v8 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

[Felipe Balbi]

Hi,

Jun Li <jun.li@xxxxxxx> writes:
>> -----Original Message-----
>> From: Baolin Wang [mailto:baolin.wang@xxxxxxxxxx]
>> Sent: Wednesday, March 30, 2016 5:31 PM
>> To: Jun Li <jun.li@xxxxxxx>
>> Cc: Peter Chen <hzpeterchen@xxxxxxxxx>; Felipe Balbi <balbi@xxxxxxxxxx>;
>> Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>; Sebastian Reichel <sre@xxxxxxxxxx>;
>> Dmitry Eremin-Solenikov <dbaryshkov@xxxxxxxxx>; David Woodhouse
>> <dwmw2@xxxxxxxxxxxxx>; Peter Chen <peter.chen@xxxxxxxxxxxxx>; Alan Stern
>> <stern@xxxxxxxxxxxxxxxxxxx>; r.baldyga@xxxxxxxxxxx; Yoshihiro Shimoda
>> <yoshihiro.shimoda.uh@xxxxxxxxxxx>; Lee Jones <lee.jones@xxxxxxxxxx>; Mark
>> Brown <broonie@xxxxxxxxxx>; Charles Keepax
>> <ckeepax@xxxxxxxxxxxxxxxxxxxxxxxxxxx>; patches@xxxxxxxxxxxxxxxxxxxxxxxxxxx;
>> Linux PM list <linux-pm@xxxxxxxxxxxxxxx>; USB <linux-usb@xxxxxxxxxxxxxxx>;
>> device-mainlining@xxxxxxxxxxxxxxxxxxxxxxxxx; LKML <linux-
>> kernel@xxxxxxxxxxxxxxx>
>> Subject: Re: [PATCH v8 0/4] Introduce usb charger framework to deal with
>> the usb gadget power negotation
>> 
>> On 30 March 2016 at 16:07, Jun Li <jun.li@xxxxxxx> wrote:
>> > Hi
>> 
>> >> On 30 March 2016 at 10:54, Jun Li <jun.li@xxxxxxx> wrote:
>> >> >> >> It is not for udc driver but for power users who want to
>> >> >> >> negotiate with USB subsystem.
>> >> >> >>
>> >> >> >
>> >> >> > 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.

-- 
balbi

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