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

[Roger Quadros <rogerq@ti.com>]

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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