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

[Jun Li]

Hi

> -----Original Message-----
> From: Baolin Wang [mailto:baolin.wang@xxxxxxxxxx]
> Sent: Wednesday, March 30, 2016 2:15 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 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.

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.

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