Re: [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection

From: Chanwoo Choi
Date: Fri Apr 10 2015 - 03:17:45 EST

Hi Robert,

On 04/09/2015 06:24 PM, Robert Baldyga wrote:
> Hi Chanwoo,
> On 04/09/2015 11:07 AM, Chanwoo Choi wrote:
>> Hi Robert,
>> On 04/09/2015 04:57 PM, Robert Baldyga wrote:
>>> Hi Chanwoo,
>>> On 04/09/2015 04:12 AM, Chanwoo Choi wrote:
>>>> Hi Robert,
>> [snip]
>>>> But, I have one question about case[3]
>>>> If id is low and vbus is high, this patch will update the state of both USB and USB-HOST cable as attached state.
>>>> Is it possible that two different cables (both USB and USB-HOST) are connected to one port simultaneously?
>>> It's because state of single USB cable connection cannot be completely
>>> described using single extcon cable. USB cable state has two bits (VBUS
>>> and ID), so we need to use two cables for single cable connection. We
>>> use following convention:
>>> cable "USB" = VBUS
>>> cable "USB-HOST" = !ID.
>> I think that extcon provider driver have to update the only one cable state
>> of either USB or USB-HOST because USB and USB-HOST feature can not be used
>> at the same time through one h/w port.
>> If extcon-usb-gpio.c update two connected event of both USB and USB-HOST cable
>> at the same time, the extcon consumer driver can not decide what handle either USB or USB-HOST.
> It can. USB OTG allows for that. Moreover device can be host even if
> ID=1 (so detected cable type is USB device), or peripheral when ID=0 (so
> detected cable type is USB host). Devices would need to have complete
> information about USB cable connection, because OTG state machine needs

As I knew, USB OTG port don't send the attached cable of both USB and USB-HOST
at the same time. The case3 in your patch update two cable state about one h/w port.

I don't agree.

> that. As I wrote, current USB cable names are misleading. It would be
> better to have "USB-VBUS" and "USB-ID".

It is strange cable name. I prefer to use only 'USB' cable name.
But, we could support the other method to get the state of whether USB-VBUS or USB-ID
by using helper API or others.

Chanwoo Choi
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