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

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Message-id: <55264148.8070903@samsung.com>
Date:	Thu, 09 Apr 2015 18:07:20 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	Robert Baldyga <r.baldyga@...sung.com>
Cc:	myungjoo.ham@...sung.com, rogerq@...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

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.

> In fact it would be better to have cables named "USB-VBUS" and "USB-ID"
> - in this convention it would be more clear.

Thanks,
Chanwoo Choi

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