Message-ID: <552E1862.6090709@ti.com>
Date:	Wed, 15 Apr 2015 10:50:58 +0300
From:	Roger Quadros <rogerq@...com>
To:	Peter Chen <peter.chen@...escale.com>,
	Chanwoo Choi <cw00.choi@...sung.com>
CC:	Robert Baldyga <r.baldyga@...sung.com>, <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>
Subject: Re: [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection

On 15/04/15 06:27, Peter Chen wrote:
> On Tue, Apr 14, 2015 at 08:29:34PM +0900, Chanwoo Choi wrote:
>> On 04/14/2015 07:38 PM, Roger Quadros wrote:
>>> 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
>>
>> Right. Robert suggested the "USB-ID" and "USB-VBUS" cable name on previous mail in mail thread.
> 
> From USB/USB-PHY driver point, it needs to know id and vbus value
> for their internal logic, so as extcon users, the cable name
> is better to reflect meaning of id and vbus, like "USB-ID" and "USB-VBUS",
> if the power is from vbus pin at USB cable, I don't think we need another
> cable name "USB-POWER" even the USB/USB-PHY driver don't need it.

I agree as well that this is the *best* option for USB case. Just because Chanwoo was
objecting these names I suggested "USB-POWER".

Chanwoo, can we simply get rid of "USB" and "USB-HOST" cables and move to
"USB-ID" and "USB-VBUS"?

The only reason you objected was saying that it is a strange cable name. Well this is
only what we care about from USB PHY drivers and user space is not interested in it
so what is the concern?

> 
>>
>>> "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.
>>
>> There is the same case for MHL cable.
>> Also, MHL cable could be connected to VBUS line.
>> - MHL : attached just MHL cable.
>> - MHL-POWER : attache MHL cable which is connected with VBUS line.
>>
>> We must need the opinion of USB/PHY driver's maintainer.
>>
>>>
>>>>
>>>> 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?
>>
>> I'm considering following functions for VBUS state. But it is my opinion,
>> If USB/PHY drivers's maintainers don't agree the new cable ("USB-POWER"),
>> We could use the following function to get VBUS state.
>> Because new cable name will affect the USB/PHY drivers.
>> - int extcon_{get|set}_vbus_state(struct extcon_dev *edev);

This is not suitable for us as USB drivers need VBUS notification event to come.
They can't keep polling for VBUS state using this API.

cheers,
-roger
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