linux-kernel - Re: [RFC 01/19] extcon: add extcon-odroid-usbotg driver

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Date:	Fri, 20 Mar 2015 16:45:49 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	Robert Baldyga <r.baldyga@...sung.com>
Cc:	Chanwoo Choi <cwchoi00@...il.com>, Roger Quadros <rogerq@...com>,
	George Cherian <gcherianv@...il.com>,
	Felipe Balbi <balbi@...com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>,
	linux-usb@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Łukasz Stelmach <l.stelmach@...sung.com>
Subject: Re: [RFC 01/19] extcon: add extcon-odroid-usbotg driver

Hi Robert,

On 03/20/2015 04:25 PM, Robert Baldyga wrote:
> Hi Chanwoo,
> 
> On 03/19/2015 09:50 PM, Chanwoo Choi wrote:
>> Hi Roger,
>>
>> On Thu, Mar 19, 2015 at 11:45 PM, Roger Quadros <rogerq@...com> wrote:
>>> On 19/03/15 14:19, George Cherian wrote:
>>>> Hi Robert,
>>>>
>>>> +Roger
>>>> On Thu, Mar 19, 2015 at 5:37 PM, Robert Baldyga <r.baldyga@...sung.com> wrote:
>>>>> Hi George,
>>>>>
>>>>> On 03/19/2015 09:50 AM, George Cherian wrote:
>>>>>> Hi Robert,
>>>>>>
>>>>>> This looks like a extcon driver based on gpio for USB.
>>>>>>
>>>>>> Roger posted a generic one a while back.
>>>>>> https://lkml.org/lkml/2015/2/2/187
>>>>>>
>>>>>> Doesn't this serve the purpose rather than adding this driver?
>>>>>
>>>>> Roger's driver doesn't support VBUS state detection so it cannot handle
>>>> I feel Roger's driver could be extended for supporting VBUS.
>>>> Also I think Roger's driver is about to get merged.
>>>> Probably, Roger or Chanwoo can better tell that
>>>
>>> It is already queued for 4.1 and is available in linux-next.
>>>
>>>>
>>>>> situation when USB cable is unpluged. In addition some of Odroid boards
>>>>> has only VBUS detection (without ID pin), so this driver cannot handle
>>>>> them at all.
>>>
>>> why not?
>>>
>>> x15-beagleboard also gets VBUS event over GPIO and I was planning to extent it
>>> to support VBUS detection.
>>
>> Sounds good to me to extent extcon-usb-gpio.c.
>> I'd like to hold only one extcon driver to support both USB and
>> USB-HOST with gpio .
>>
>> There are one more extcon-gpio driver in mailing list as following:
>> - extcon-usb-gpio.c (will be merged to Linux 4.1)
>> - extcon-odroid-usbotg.c
>> - extcon-otg_gpio.c [1]
>> [1] https://lkml.org/lkml/2015/2/19/411
>>
>> The each extcon gpio driver support both USB/USB-HOST cable by using
>> different way,
>> Because some board which detect USB/USB-HOST by gpio have a little
>> different pin composition
> 
> These differences are small. In general we have three cases:
> 
> 1. We have both VBUS and ID pin detection - we can detect USB, USB-HOST
> and cable disconnection.
> 
> 2. We have only VBUS detection - we can detect USB and cable disconnection.
> 
> 3. We have ID pin only - we can distinguish between USB and USB-HOST but
> without ability to detect cable disconnection.
> 
>>
>> I think only one extcon driver can support all cases with optional properties.
> 
> So my driver in current form is ready for that. Only thing it would need
> to change is to make VBUS detection an option (for now is mandatory
> because all of supported Odroid boards have it). Then boards with VBUS
> detection only or ID pin detection only will be handled also. I can also
> change name of the driver to more generic. I'm going to prepare V2 on my
> patches today.

Could you implement this feature on extcon-usb-gpio.c to support various pin composition?
because extcon-usb-gpio.c was already implemented by Roger.
If you implement other extcon driver to detect USB/USB-HOST cable by using gpio,
there will be similar two extcon gpio driver for USB cable.

And,
As Roger comment, he have the plan to extend the extcon-usb-gpio.c.
So, If you will implement some feature for extcon driver with gpio,
I'd like you to share your plan this thread to remove duplicat work.

Thanks,
Chanwoo Choi

> 
> Thanks,
> Robert Baldyga
> 
>>
>> Roger,
>> I'd like you to share your plan to extent the extcon-usb-gpio.c for
>> removing duplicate work.
>>
>> [snip]
>>
>> Thanks,
>> Chanwoo Choi
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> 
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