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

From: Chanwoo Choi <cw00.choi@samsung.com>
To: Robert Baldyga <r.baldyga@samsung.com>
Cc: myungjoo.ham@samsung.com, rogerq@ti.com,
	linux-usb@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, m.szyprowski@samsung.com
Subject: Re: [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection
Date: Fri, 10 Apr 2015 16:17:36 +0900	[thread overview]
Message-ID: <55277910.2070000@samsung.com> (raw)
In-Reply-To: <55264534.4020006@samsung.com>

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.

Thanks,
Chanwoo Choi