Message-ID: <552CE5C0.3010207@ti.com>
Date:	Tue, 14 Apr 2015 13:02:40 +0300
From:	Roger Quadros <rogerq@...com>
To:	Chanwoo Choi <cw00.choi@...sung.com>,
	Robert Baldyga <r.baldyga@...sung.com>
CC:	<myungjoo.ham@...sung.com>, <linux-usb@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<m.szyprowski@...sung.com>, "Balbi, Felipe" <balbi@...com>,
	"ABRAHAM, KISHON VIJAY" <kishon@...com>,
	Peter Chen <peter.chen@...escale.com>
Subject: Re: [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection

Fixed Kishon's id.

On 14/04/15 13:01, Roger Quadros wrote:
> On 10/04/15 12:18, 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.
> 
> Now it is starting to look like existing extcon states are not suitable for USB/PHY drivers to deliver
> VBUS and ID information reliably.
> This is because based on your comments the "USB" and "USB-HOST" states look like some fuzzy states
> and have no direct correspondence with "VBUS" and "ID". The fact that they can't become
> attached simultaneously makes me conclude that "USB" and "USB-HOST" cable states are really 
> capturing only the ID pin state.
> 
> I can suggest the following options
> a) let "USB" and "USB-HOST" only indicate ID pin status. Add a new cable state for "VBUS" notification.
> Maybe call it "USB-POWER" or something.
> 
> NOTE: "USB-POWER" can become attached simultaneously with "USB" or "USB-HOST". But "USB-POWER" is now really
> a different cable like "Fast-Charger" or "Slow-Charger".
> 
> b) stop using extcon framework for USB VBUS and ID notification.
> 
> cheers,
> -roger
> 
>>
>>>
>>>>
>>>>>
>>>>>> 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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>>
> 

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