Date:	Fri, 20 Mar 2015 08:25:27 +0100
From:	Robert Baldyga <r.baldyga@...sung.com>
To:	Chanwoo Choi <cwchoi00@...il.com>, Roger Quadros <rogerq@...com>
Cc:	George Cherian <gcherianv@...il.com>, Felipe Balbi <balbi@...com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>,
	Chanwoo Choi <cw00.choi@...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 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.

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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