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

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Message-ID: <7ca666e4-545e-6057-bed3-db45997b255d@ti.com>
Date:	Mon, 1 Aug 2016 15:23:46 +0300
From:	Roger Quadros <rogerq@...com>
To:	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@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-samsung-soc@...r.kernel.org>
CC:	Peter Chen <peter.chen@...escale.com>,
	"Ivan T. Ivanov" <iivanov@...sol.com>,
	Felipe Balbi <balbi@...nel.org>, <kishon@...com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [RFC v4 0/7] extcon: usb-gpio: fixes and improvements

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?

cheers,
-roger