linux-kernel - Re: [PATCH v4] extcon: gpio: Add the support for Device tree bindings

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Date:	Tue, 31 May 2016 16:35:03 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	Rob Herring <robh@...nel.org>,
	Venkat Reddy Talla <vreddytalla@...dia.com>
Cc:	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	devicetree@...r.kernel.org, Kumar Gala <galak@...eaurora.org>,
	linux-kernel@...r.kernel.org,
	Laxman Dewangan <ldewangan@...dia.com>
Subject: Re: [PATCH v4] extcon: gpio: Add the support for Device tree bindings

Hi Rob,

On 2016년 05월 31일 15:44, Chanwoo Choi wrote:
> On 2016년 05월 28일 00:29, Rob Herring wrote:
>> On Thu, May 26, 2016 at 05:17:45PM +0530, Venkat Reddy Talla wrote:
>>> Add the support for Device tree bindings of extcon-gpio driver.
>>> The extcon-gpio device tree node must include the both 'extcon-id' and
>>> 'gpios' property.
>>
>> I think extcon bindings are a mess in general...
>>
>>> For example:
>>> 	usb_cable: extcon-gpio-0 {
>>> 		compatible = "extcon-gpio";
>>> 		extcon-id = <EXTCON_USB>;
>>> 		gpios = <&gpio6 1 GPIO_ACTIVE_HIGH>;
>>> 	}
>>> 	ta_cable: extcon-gpio-1 {
>>> 		compatible = "extcon-gpio";
>>> 		extcon-id = <EXTCON_CHG_USB_DCP>;
>>> 		gpios = <&gpio3 2 GPIO_ACTIVE_LOW>;
>>> 		debounce-ms = <50>;	/* 50 millisecond */
>>> 		wakeup-source;
>>> 	}
>>
>> This is all 1 logical connector, the USB connector. Why are you 
>> describing cables? Those are not part of the h/w and are dynamic. 
>> Describe this as a connector which is one thing (i.e. node). Use a 
>> compatible string that reflects the type of connector 
>> (usb-microab-connector), not the driver you want to use. Then define 
>> GPIO lines needed to provide state information like VBus, ID, charger 
>> modes and control lines like soft connect (D+ pullup enable), VBus 
>> enable, etc.
> 
> You're right. The extcon-gpio driver will not use the "extcon-gpio" raw compatible.
> As you commented[1], the each connector will have the unique name to use the extcon-gpio.c driver.
> [1] https://lkml.org/lkml/2015/10/21/906
> 
> 
> For example,
> The extcon-gpio.c driver may have the different name including the h/w information
> according to the kind of external connector.
> 
> static const struct of_device_id gpio_extcon_of_match[] = {
> 	{
> 		.compatible = "extcon-chg-sdp",	/* SDP charger connector */
> 		.data = EXTCON_CHG_SDP_DATA,
> 	}, {
> 		.compatible = "extcon-chg-dcp",	/* DCP charger connector */
> 		.data = EXTCON_CHG_DCP_DATA,
> 	}, {
> 		.compatible = "extcon-jack-microphone", /* Microphone jack connector */
> 		.data = EXTCON_JACK_MICROPHONE_DATA,
> 	}, {
> 		.compatible = "extcon-disp-hdmi", /* HDMI connector*/
> 		.data = EXTCON_DISP_HDMI_DATA,
> 	},
> 	......
> };

I reply it again.

The extcon-gpio.c is very similar with existing gpio_keys.c driver[1]
[1] drivers/input/keyboard/gpio_keys.c

The gpio_keys.c driver use the following style to support the device-tree.
It use the "gpio-keys" compatible and this dt node include the specific
'key code' such as 'extcon-id = <EXTCON_CHG_USB_DCP>;'

	gpio_keys {
		compatible = "gpio-keys";

		power_key {
			gpios = <&gpx2 7 GPIO_ACTIVE_LOW>;
			linux,code = <KEY_POWER>;
			label = "power key";
			debounce-interval = <10>;
			wakeup-source;
		};
	};

If the extcon-gpio.c driver should have the separate compatible according to
the kind of external connector, the list of compatible name of extcon-gpio.c driver
will be increased when new external connector is attached.

The extcon-gpio.c driver can separate the kind of external connector
by using the 'extcon-id' property. 

Thanks,
Chanwoo Choi