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

Baolin Wang
2016-03-31T05:33:27Z

On 30 March 2016 at 19:24, Felipe Balbi <balbi@kernel.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()'.

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.

>
> --
> balbi

--
Baolin.wang
Best Regards