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: Thursday, March 31, 2016 1:23 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 18:58, Jun Li <jun.li@xxxxxxx> 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
> > 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().

> 
> --
> Baolin.wang
> Best Regards