linux-kernel - Re: [PATCH 2/2] extcon: Add the support of EXTCON_CHG_USB when SDP port is attached or detached

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Message-ID: <5613BD10.3070300@ti.com>
Date:	Tue, 6 Oct 2015 15:22:40 +0300
From:	Roger Quadros <rogerq@...com>
To:	Chanwoo Choi <cw00.choi@...sung.com>,
	<linux-kernel@...r.kernel.org>
CC:	<k.kozlowski@...sung.com>, <ckeepax@...nsource.wolfsonmicro.com>,
	<gregkh@...uxfoundation.org>, <ramakrishna.pallala@...el.com>,
	<patches@...nsource.wolfsonmicro.com>, <myungjoo.ham@...sung.com>
Subject: Re: [PATCH 2/2] extcon: Add the support of EXTCON_CHG_USB when SDP
 port is attached or detached

Chanwoo,

On 06/10/15 15:12, Chanwoo Choi wrote:
> Roger,
> 
> On 2015년 10월 06일 20:49, Roger Quadros wrote:
>> Hi,
>>
>> On 06/10/15 14:21, Chanwoo Choi wrote:
>>> The SDP (Standard Downstream Port) is one of various USB Charging ports. The SDP
>>> supports both the data transmission and the charging through USB connector at
>>> the same time. So, the EXTCON framework defines two connector type for USB SDP
>>> connector as following:
>>> - EXTCON_USB means the USB cable for data transmission.
>>> - EXTCON_CHG_USB means the USB charger cable for battery charging.
>>>
>>> This patch add the support of EXTCON_CHG_USB when USB SDP is attached or
>>> detached.
>>
>> I didn't understand why this change is needed. SDP, EXTCON_USB and EXTCON_CHG_USB
>> are the same thing. no?
> 
> As you knew, SDP support both data transmission and charging
> through one port at the same time. Also, On patch1 of this patch-set,
> I add the prefix to clarify both attribute and meaning of external connector as following:
> - EXTCON_CHG_* mean the charger connector.
> 
> So, there are three possible naming approach for USB SDP.
> 
> Approach 1.
> - EXTCON_USB		/* SDP for both data transmission and charging */
> 
> Approach 2.
> - EXTCON_USB		/* SDP for data transmission */
> - EXTCON_CHG_USB	/* SDP for charging */

This only adds confusion. There is only one cable that will always do both jobs
so no point in using 2 names for it.

> 
> Approach 3.
> - EXTCON_CHG_USB	/* SDP for both data transmission and charging */
> 
> It is not fixed about name. I want to discuss what is proper name for USB SDP.

I do not have any preference over 1 or 3.

cheers,
-roger
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