linux-kernel - Re: [PATCH v2 1/2] extcon: Add extcon_set_cable_line_state() to inform the additional state of external connectors

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Date:	Fri, 29 May 2015 16:58:34 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	"Ivan T. Ivanov" <iivanov@...sol.com>
Cc:	Roger Quadros <rogerq@...com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Robert Baldyga <r.baldyga@...sung.com>,
	Peter Chen <peter.chen@...escale.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Felipe Balbi <balbi@...com>,
	"myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>
Subject: Re: [PATCH v2 1/2] extcon: Add extcon_set_cable_line_state() to inform
 the additional state of external connectors

On 05/28/2015 06:37 PM, Ivan T. Ivanov wrote:
> Hi, 
> 
> On Thu, 2015-05-28 at 18:17 +0900, Chanwoo Choi wrote:
>>
>>
>> 2015년 5월 28일 목요일, Ivan T. Ivanov<iivanov@...sol.com>님이 작성한 메시지:
>>> Hi Chanwoo,
>>>
>>> On Thu, 2015-05-28 at 00:06 +0900, Chanwoo Choi wrote:
>>>> On Wed, May 27, 2015 at 11:38 PM, Roger Quadros <rogerq@...com> wrote:
>>>>> Chanwoo,
>>>>>
>>>>> On 27/05/15 15:15, Chanwoo Choi wrote:
>>>>>> This patch adds the extcon_set_cable_line_state() function to inform
>>>>>> the additional state of each external connector and 'enum
>>>>>> extcon_line_state'
>>>>>> enumeration which include the specific states of each external connector.
>>>>>>
>>>>>> The each external connector might need the different line state. So,
>>>>>> current
>>>>>> 'extcon_line_state' enumeration contains the specific state for USB as
>>>>>> following:
>>>>>>
>>>>>> - Following the state mean the state of both ID and VBUS line for USB:
>>>>>> enum extcon_line_state {
>>>>>>         EXTCON_USB_ID_LOW       = BIT(1),       /* ID line is low. */
>>>>>>         EXTCON_USB_ID_HIGH      = BIT(2),       /* ID line is high. */
>>>>>
>>>>>
>>>>> ID_LOW and ID_HIGH cannot happen simultaneously so they can use the same bit
>>>>> position.
>>>>> if the bit is set means it is high, if it is cleared means it is low.
>>>>
>>>> These are the notifier event. So, extcon_line_state have to include
>>>> each event for both low or high state of ID.
>>>> because the extcon consumer driver using the
>>>> extcon_register_notifier() need the each event to distinguish the type
>>>> of event.
>>>>
>>>>>>         EXTCON_USB_VBUS_LOW     = BIT(3),       /* VBUS line is low. */
>>>>>>         EXTCON_USB_VBUS_HIGH    = BIT(4),       /* VBUS line is high. */
>>>>>
>>>>>
>>>>> same here.
>>>>
>>>> ditto.
>>>>
>>>>> enum doesn't look like the right type for extcon_line_state as it is more of
>>>>> a bitmask.
>>>>
>>>> Why? I prefer to use the enum if there are no problem.
>>>
>> If you insist your opinion, you shoud suggest the reason. Could you tell me the reason?
> 
> It looks unreadable. There is no need to mix interface API (enum extcon_line_state)
> with implementation details. You can use plain enum at interface level and hide
> shifting inside implementation.

OK, I define it instead of enum.

> 
>>
>>
>>>>>>
>>>>>> +enum extcon_line_state {
>>>>>> +       /* Following two definition are used for whether external
>>>>>> connectors
>>>>>> +        * is attached or detached. */
>>>>>> +       EXTCON_DETACHED         = 0x0,
>>>>>> +       EXTCON_ATTACHED         = 0x1,
>>>>>> +
>>>>>> +       /* Following states are only used for EXTCON_USB. */
>>>>>> +       EXTCON_USB_ID_LOW       = BIT(1),       /* ID line is low. */
>>>>>> +       EXTCON_USB_ID_HIGH      = BIT(2),       /* ID line is high. */
>>>>>> +       EXTCON_USB_VBUS_LOW     = BIT(3),       /* VBUS line is low. */
>>>>>> +       EXTCON_USB_VBUS_HIGH    = BIT(4),       /* VBUS line is high. */
>>>>>> +};
>>>>>
>>>>>
>>>>> Why do you use enum? How about the following bit definitions for line state.
>>>>>
>>>>> #define EXTCON_ATTACHED_DETACHED_BIT    BIT(0)
>>>>> #define EXTCON_USB_ID_BIT               BIT(1)
>>>>> #define EXTCON_USB_VBUS_BIT             BIT(2)
>>>>> ...
>>>>>
>>>>> code must check if appropriate bit is set or cleared to get the high/low
>>>>> state.
>>>>
>>>> I answer about it on upper.
>>>>
>>>
>>> Funny. We can use the one bit for DETACHED/ATTACHED, but we
>> hmm. Did you read my answer about low/high?
>>
>> But, I'm considering again about using the detached/attached value.
> 
> Ok, but consumers will receive one event at time, right?

Yes.

Cheers,
Chanwoo Choi
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