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

[Jun Li]

> -----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 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.

> In the 'usb_charger_detect_type()', it
> usually get the charger type from type registers has been done by hardware
> from PMIC, which can not affect the DP/DM line.
> 
> >
> > Li Jun
> >
> >>
> >> > think it's necessary to check charger type at every event from usb
> >> gadget.
> >>
> >> My meaning is not every event from usb gadget. When the usb gadget
> >> state changes or the extcon device (maybe GPIO detection) state
> >> changes, which means charger plugin or pullup, we need to check the
> >> charger type to set current.
> >
> > From your below code, you call usb_charger_notify_others() in every
> > state change.
> 
> I think it does not matter. In case the usb charger missed some gadget
> state changes. Or I replace it with 'USB_STATE_CONFIGURED' state.
> Thanks.
> 
> >
> > if (uchger->old_gadget_state != state) {
> >         uchger->old_gadget_state = state;
> >
> >         if (state >= USB_STATE_ATTACHED)
> >                 uchger_state = USB_CHARGER_PRESENT;
> >         else if (state == USB_STATE_NOTATTACHED)
> >                 uchger_state = USB_CHARGER_REMOVE;
> >         else
> > /* this else will never happen */
> >                 uchger_state = USB_CHARGER_DEFAULT;
> >
> >         usb_charger_notify_others(uchger, uchger_state); }
> >
> >>
> >> > Something in gadget driver you can utilize is only vbus detection,
> >> > and report diff current by diff usb state if it's a SDP.
> >>
> >> --
> >> Baolin.wang
> >> Best Regards
> 
> 
> 
> --
> Baolin.wang
> Best Regards