Message-id: <55279550.1060609@samsung.com>
Date: Fri, 10 Apr 2015 18:18:08 +0900
From: Chanwoo Choi <cw00.choi@samsung.com>
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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
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On 04/10/2015 05:46 PM, Robert Baldyga wrote:
> On 04/10/2015 10:10 AM, Chanwoo Choi wrote:
>> On 04/10/2015 04:45 PM, Robert Baldyga wrote:
>>> On 04/10/2015 09:17 AM, Chanwoo Choi wrote:
>>>> 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.
>>>>
>>>
>>> It's because simple "USB" or "USB-HOST" means nothing for USB OTG
>>> machine. It needs to know exact VBUS and ID states, which cannot be
>>> concluded basing on cable type only. That's why I have used "USB-HOST"
>>> name together with "USB" to pass additional information about USB cable
>>> connection.
>>
>> I think this method is not proper to support this case.
>> It may cause the confusion about other case using USB/USB-HOST cable state
>> except of you commented case.
> 
> That's why I finally proposed to use "USB-ID" and "USB-VBUS" in parallel
> with old names. It seems to be simpler solution than adding new
> mechanism notifying about VBUS and ID states changes.


As I commented on previous reply, I don't agree to use 'USB-ID' and 'USB-VBUS'.
If we add new strange 'USB-ID' and 'USB-VBUS' name, we would add non-general cable
name continuoulsy.

I think that extcon core provide the helper API to get the value of VBUS.
But I need to consider it.

> 
>>
>>>
>>>> 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.
>>>>
>>>
>>> Ok, so do you have any idea how to do it? Do we want to supply
>>> additional API for notifying about VBUS and ID changes?
>>
>> No, we need to consider more standard solution to support this case.
>>
> 
> Thanks,
> Robert Baldyga
> 
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