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

[Roger Quadros <rogerq@ti.com>]

On 14/04/15 13:31, Chanwoo Choi wrote:
> On 04/14/2015 07:02 PM, Roger Quadros wrote:
>> 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.
> 
> We must discuss it before using the new cable name
> such as "USB-POWER", "USB-ID" and "USB-VBUS".

I didn't say to add "USB-ID" or "USB-VBUS". solution (a) was to have the following
"USB" - attached means ID is high. i.e. Type-B plug attached.
"USB-HOST" - attached means ID is low. i.e. Type-A plug attached.
"USB-POWER" - attached means USB power is present. i.e. VBUS is alive.

This way the definition of USB and USB-HOST remain true to their name and avoid further confusions.
VBUS state is got through the "USB-POWER" cable state.

> 
> What is the appropriate method of following two solution?
> - Fisrt, use the new cable name "USB-*".
I explained this above.

> - Second, use the additional API to get the VBUS state.

You keep mentioning additional API for VBUS. But I don't see any such API. Can you please
suggest what API you are talking about?

cheers,
-roger


> 
> Cheers,
> Chanwoo Choi
> 
>>>
>>> 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.
> 
>