linux-kernel - Re: [RFC v4 0/7] extcon: usb-gpio: fixes and improvements

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Date:	Mon, 1 Aug 2016 21:57:37 +0900
From:	Chanwoo Choi <cwchoi00@...il.com>
To:	Roger Quadros <rogerq@...com>
Cc:	Chanwoo Choi <cw00.choi@...sung.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Kukjin Kim <kgene@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	devicetree <devicetree@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Peter Chen <peter.chen@...escale.com>,
	"Ivan T. Ivanov" <iivanov@...sol.com>,
	Felipe Balbi <balbi@...nel.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [RFC v4 0/7] extcon: usb-gpio: fixes and improvements

Hi Roger,

2016-08-01 21:23 GMT+09:00 Roger Quadros <rogerq@...com>:
> Hi,
>
> On 09/06/16 12:32, Chanwoo Choi wrote:
>> Hi,
>>
>> On 2016년 06월 09일 17:39, Krzysztof Kozlowski wrote:
>>>
>>> Hi,
>>>
>>>
>>> On 06/09/2016 10:35 AM, Chanwoo Choi wrote:
>>>> Hi,
>>>>
>>>> It is good to support USB_ID and USB_VBUS by extcon.
>>>>
>>>> But,
>>>> there is some issue about adding the new cable type for
>>>> both EXTCON_USB_ID and EXTCON_USB_VBUS
>>>>
>>>> I think that the ID and VBUS state are not cable type
>>>> Instead, ID and VBUS state are the property of USB cable.
>>>>
>>>> So, I'd like to add the following function to support
>>>> the property of each cable as following:
>>>> The client driver can get the state of property by using
>>>> the extcon_get_cable_property_state().
>>>>
>>>> - int extcon_get_cable_property_state(struct extcon_dev *edev,
>>>>                             unsigned int id,
>>>>                             enum extcon_property property);
>>>> - int extcon_set_cable_property_state(struct extcon_dev *edev,
>>>>                             unsigned int id,
>>>>                             enum extcon_property property,
>>>>                             unsigned int state);
>>>>
>>>> For example,
>>>> In extcon-usb-gpio.c, set state of property as follwoing:
>>>>     extcon_set_cable_property_state(edev, EXTCON_USB, EXTCON_USB_PROP_ID, 1);
>>>>     extcon_set_cable_property_state(edev, EXTCON_USB, EXTCON_USB_PROP_VBUS, 1);
>>>>
>>>>
>>>> In the extcon client driver, get state of property as following:
>>>>     id_state = extcon_get_cable_property_state(edev, EXTCON_USB, EXTCON_USB_PROP_ID);
>>>>     vbus_state = extcon_get_cable_property_state(edev, EXTCON_USB, EXTCON_USB_PROP_VUBS);
>>>
>>> How one can receive notifications with this API?
>>
>> I think that the extcon don't support the notification only for property.
>> When USB or USB_HOST cable state is changed, the client driver
>> call the extcon_get_cable_property_state() to read the state of property.
>>
>> Namely, the property depend on the specific external connector.
>>
>>>
>>> Last time you wrote, at the end of discussion:
>>> http://thread.gmane.org/gmane.linux.kernel/1923192/focus=1923193
>>>> IMO, if some usb driver check both id and vbus pin at the same time,
>>>> the usb driver can know the both id and vbus pin state through only
>>> one notifier event.
>>>>
>>>> Also,
>>>> If some usb driver want to know the state of id pin except of vbus state,
>>>> when receiving following events, id pin is low.
>>>>     #define EXTCON_USB_ID_L_VBUS_L0
>>>>     #define EXTCON_USB_ID_L_VBUS_H1
>>>> when receiving following events, id pin is high.
>>>>     #define EXTCON_USB_ID_H_VBUS_L2
>>>>     #define EXTCON_USB_ID_H_VBUS_H3
>>>> Also, some usb driver would catch the vbus pin state with same method.
>>>>
>>>> But, it is just my opinion. We may use following notifier events for
>>> each pin.
>>>> We need to discuss it.
>>>>     #define EXTCON_USB_ID_LOW
>>>>     #define EXTCON_USB_ID_HIGH
>>>>     #define EXTCON_USB_VBUS_LOW
>>>>     #define EXTCON_USB_VBUS_HIGH
>>>
>>> ... all other participants agreed on that conclusion. So why change of
>>> view point now?
>>
>> Unitl now, the extcon framework only handle the state of external connector(cable).
>> - The state of external connector is either attached or detached.
>>
>> I think that ID and VBUS are not external connector(cable).
>> The ID and VBUS are more appropriate as property than new type of external connector.
>>
>
> Was there any conclusion on how we can support raw ID and VBUS events with extcon?

The extcon will support the USB_ID and USB_VBUS as extcon property.
I'm sending the patches[1] for extcon property.

[1] https://lkml.org/lkml/2016/8/1/25
: [PATCH v2 0/6] extcon: Add the support for extcon type and property

Thanks,
Chanwoo Choi