Message-id: <55279B03.7060202@samsung.com>
Date: Fri, 10 Apr 2015 11:42:27 +0200
From: Robert Baldyga <r.baldyga@samsung.com>
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To: Chanwoo Choi <cw00.choi@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
References: <1427980385-21285-1-git-send-email-r.baldyga@samsung.com>
 <1427980385-21285-3-git-send-email-r.baldyga@samsung.com>
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 <55264148.8070903@samsung.com> <55264534.4020006@samsung.com>
 <55277910.2070000@samsung.com> <55277FA2.6090700@samsung.com>
 <55278580.2090809@samsung.com> <55278DD3.3020409@samsung.com>
 <55279550.1060609@samsung.com>
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On 04/10/2015 11:18 AM, Chanwoo Choi wrote:
> 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.

We need more than API for getting VBUS value - we need to be notified
about its changes, because if we don't distinguish between USB-HOST with
VBUS on, and USB-HOST with VBUS off, then we will not receive
notification from extcon at VBUS state change.

Thanks,
Robert Baldyga
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