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

[Felipe Balbi <balbi@kernel.org>]

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Hi,

Baolin Wang <baolin.wang@linaro.org> writes:
> [ text/plain ]
> 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()'.

yes.

> 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.

they shouldn't detect is get_type(), the semantics doesn't work. If, at
some point, we have to do SW detection of the charger, then a new
->charger_detect() method will have to be added.

-- 
balbi

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