From: Roger Quadros <rogerq@ti.com>
To: Guenter Roeck <groeck@google.com>, Chanwoo Choi <cw00.choi@samsung.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Felipe Balbi <balbi@kernel.org>, <myungjoo.ham@samsung.com>,
Chris Zhong <zyw@rock-chips.com>,
Guenter Roeck <groeck@chromium.org>, <chanwoo@kernel.org>,
Krzysztof Kozlowski <k.kozlowski@samsung.com>
Subject: Re: [PATCH v3 2/6] extcon: Add the support for extcon property according to extcon type
Date: Thu, 4 Aug 2016 11:49:36 +0300 [thread overview]
Message-ID: <565b50ac-7b34-740f-ca59-88c3b95bfe82@ti.com> (raw)
In-Reply-To: <CABXOdTcjrCzpVhEq7qGk6stkd66c92MGtP9_prT-wpGn3Rp9Dw@mail.gmail.com>
On 04/08/16 07:09, Guenter Roeck wrote:
> On Wed, Aug 3, 2016 at 5:42 PM, Chanwoo Choi <cw00.choi@samsung.com> wrote:
>> Hi Roger,
>>
>> On 2016년 08월 03일 18:46, Roger Quadros wrote:
>>> Hi Chanwoo,
>>>
>
> [ ... ]
>
>>>>>> + /*
>>>>>> + * Check whether the external connector is attached.
>>>>>> + * If external connector is detached, the user can not
>>>>>> + * get the property value.
>>>>>> + */
>>>>>
>>>>> How will this work for USB case? We need to know VBUS and ID states
>>>>> even if the USB cable is detached.
>>>>
>>>> When USB is detached, extcon_get_property return the default value without any operation.
>>>> The default value of supported property are 0 (zero). If new property need the differnt default
>>>> value, I'll support it.
>>>
>>> Is the property a property of the connector or of the cable?
>>>
>>> In my opinion, ID and VBUS are properties of the USB connector and not of
>>> the USB cable. So extcon must provide valid status for those properties
>>> even if USB cable or USB_HOST cable is detached.
>>
>> I don't understand about that if USB and USB_HOST are detached,
>> how can the USB be operating? As you mentioned that, extcon must
>> provide the valid status for both state and properties.
>>
>
> Correct. No cable means that the polarity is unknown, and VBUS must not be
> active (for USB_HOST), or it can not be active (for USB).
OK.
>
> Only question might be EXTCON_PROP_USB_ID; I am not sure I understand
> what it is supposed to return. Maybe it would be worthwhile to document it ?
Agreed. It seems redundant as ID can be easily inferred from USB_HOST cable state.
i.e. if USB_HOST is attached ID is 0. If USB_HOST is detached ID is 1.
>
>> So, I already mentioned, When USB and USB_HOST are detached,
>> extcon return the default value instead of error value.
>> I think that it is reasonable. Why is it not a valid?
>>
>
> I agree; I don't know what else could be returned if no cable is
> attached, even if we wanted to.
>
OK.
I understood now that if kernel USB driver can interpret EXTCON_USB, EXTCON_USB_HOST
and VBUS property, it sufficiently captures ID and VBUS information.
cheers,
-roger
next prev parent reply other threads:[~2016-08-04 8:57 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-02 1:58 [PATCH v3 0/6] extcon: Add the support for extcon type and property Chanwoo Choi
2016-08-02 1:58 ` [PATCH v3 1/6] extcon: Add the extcon_type to gather each connector into five category Chanwoo Choi
2016-08-02 7:27 ` Roger Quadros
2016-08-02 7:41 ` Chanwoo Choi
2016-08-02 1:58 ` [PATCH v3 2/6] extcon: Add the support for extcon property according to extcon type Chanwoo Choi
2016-08-02 7:43 ` Roger Quadros
2016-08-02 8:08 ` Chanwoo Choi
2016-08-03 9:46 ` Roger Quadros
2016-08-04 0:42 ` Chanwoo Choi
2016-08-04 4:09 ` Guenter Roeck
2016-08-04 8:49 ` Roger Quadros [this message]
2016-08-04 10:57 ` Chanwoo Choi
2016-08-04 14:47 ` Guenter Roeck
2016-08-05 0:33 ` Chanwoo Choi
2016-08-02 1:58 ` [PATCH v3 3/6] extcon: Add the support for the capability of each property Chanwoo Choi
2016-08-02 8:07 ` Roger Quadros
2016-08-02 8:18 ` Chanwoo Choi
2016-08-02 1:58 ` [PATCH v3 4/6] extcon: Rename the extcon_set/get_state() to maintain the function naming pattern Chanwoo Choi
2016-08-02 1:58 ` [PATCH v3 5/6] extcon: Add the synchronization extcon APIs to support the notification Chanwoo Choi
2016-08-02 1:58 ` [PATCH v3 6/6] extcon: Add EXTCON_DISP_DP and the property for USB Type-C Chanwoo Choi
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