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

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Message-id: <57592B4A.4000407@samsung.com>
Date:	Thu, 09 Jun 2016 10:39:38 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Chanwoo Choi <cw00.choi@...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:	rogerq@...com, Peter Chen <peter.chen@...escale.com>,
	"Ivan T. Ivanov" <iivanov@...sol.com>, balbi@...com, kishon@...com,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [RFC v4 0/7] extcon: usb-gpio: fixes and improvements


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?

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?

Best regards,
Krzysztof