Message-ID: <552F61B2.8000608@ti.com>
Date:	Thu, 16 Apr 2015 10:16:02 +0300
From:	Roger Quadros <rogerq@...com>
To:	Chanwoo Choi <cw00.choi@...sung.com>,
	Peter Chen <peter.chen@...escale.com>,
	"Balbi, Felipe" <balbi@...com>,
	"ABRAHAM, KISHON VIJAY" <kishon@...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>
Subject: Re: [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection

On 16/04/15 10:00, Chanwoo Choi wrote:
> Hi Peter,
> 
> On 04/16/2015 10:59 AM, Peter Chen wrote:
>> On Wed, Apr 15, 2015 at 06:26:23PM +0900, Chanwoo Choi wrote:
>>> Hi Roger and Peter,
>>>
>>> On 04/15/2015 04:50 PM, Roger Quadros wrote:
>>>> 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"?
>>>
>>> I'm wondering about changing the previous cable name from 'USB'/'USB-HOST'
>>> to 'USB-ID/USB-VBUS' because extcon framework update the state of cable by
>>> using uevent and the user-space process would catch the changed state by
>>> using cable name ('USB'/'USB-HOST').
>>>
>>> The user-space process may not consider the both id and vbus of USB.
>>> If 'USB-ID'/'USB-VBUS' cable name is used instead of 'USB'/'USB-HOST',
>>> It may cause the confusion about what is meaning of cable name
>>> on user-space process.
>>
>> >From the user point, maybe the name of 'USB-OTG' is more suitable
>> due to below reasons:
>> - The users usually call this Micro-AB cable as 'USB-OTG' cable
>> - When this Micro-AB cable is inserted, the current port may will work as
>> host role, but if OTG HNP is supported, this port may be switched to device
>> role on the fly, eg, use case like Apple Carplay.
> 
> OK. I agree that using the 'USB-OTG' cable name instead of 'USB-HOST'.
> - 'USB' for usb device
> - 'USB-HOST' -> 'USB-OTG' for usb host

I'm lost now.
Can you please explain when and based on what these cables should become attached and detached?

What is user space really interested in?
- Does it only care that USB cable is attached/detached
- does it want to know what type of cable is attached (Type-A, Type-B)
- does it want to know what mode the USB is working on (host, device)

I'm getting a feeling that we have not fully understood the problem and we are already
trying to solve it.

cheers,
-roger

> 
>>
>>>
>>> So,
>>> I prefer to use existing 'USB' and 'USB-HOST' cable name.
>>> and then want to add additional method to get the vbus state.
>>>
>>> I think two following method to get the vbus state.
>>> 1) Add the extcon_{get|set}_vbus_state()
>>> - extcon_{get|set}_vbus_state()
>>> - the list of of return value
>>> 	#define EXTCON_USB_VBUS_OFF	0
>>> 	#define EXTCON_USB_VBUS_ON	1
>>>
>>> When USB/USB-HOST is attached and receive the notification onextcon consumer driver
>>> ,extcon consumer driver would get the vbus state by extcon_get_vbus_state().
>>>
>>> 2) Add the notifier chain for vbus state update
>>> - extcon_{register|unregister}_vbus_notifier()
>>> - the list of notifier event
>>> 	#define EXTCON_USB_VBUS_OFF	0
>>> 	#define EXTCON_USB_VBUS_ON	1
>>>
>>
>> Ok, from USB point, external id/vbus value can't decide
>> which role the controller will be, the controller driver 
>> will decide role according to many things, eg, user configurations,
>> id/vbus value, OTG HNP, etc.
>>
>> So, from USB controller/phy driver, it doesn't care which cable is
>> inserted, it cares about id/vbus value. Eg, it can get id/vbus value
>> and it will be notified when the id/vbus value has changed.
> 
> OK, I change the notifier name and add notifier events as following:
> 
> - extcon_{register|unregister}_usb_notifier(struct extcon_dev *edev, struct notifier_block *nb);
> - list of notifier events
> 	#define EXTCON_USB_ID_L_VBUS_L	0	/* ID low  and VBUS low */
> 	#define EXTCON_USB_ID_L_VBUS_H	1	/* ID low  and VBUS high */
> 	#define EXTCON_USB_ID_H_VBUS_L	2	/* ID high and VBUS low */
> 	#define EXTCON_USB_ID_H_VBUS_H	3	/* ID high and VBUS high */
> 
> I think that we need the opinion of Felipe and Kishon about this notifier chain.
> 
>>
>>>
>>> 3) add the new cable 'USB-POWER' by Roger suggestion .
>>> - When 'USB-POWER' cable is attached, extcon will update the cable state
>>> 'USB-POWER' means only the vbus state. But, 'USB-POWER' is not h/w cable.
>>> The user-space process would handle this uevent of 'USB-POWER'
>>> such as h/w cable's uevent. I think it is not clear on the user-space process aspect.
>>
>> Would you explain the user for 'USB-POWER', and what it stands for from
>> user point?
> 
> IMO, I think '*-POWER' keyword is not standard cable name on the user-space.
> As I commend on upper reply, I agree USB/USB-OTG cable name.
> 
> [snip]
> 
> Thanks,
> Chanwoo Choi
> 

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