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

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Date:	Tue, 31 May 2016 08:35:22 -0500
From:	Rob Herring <robh@...nel.org>
To:	Chanwoo Choi <cw00.choi@...sung.com>
Cc:	Venkat Reddy Talla <vreddytalla@...dia.com>,
	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" <devicetree@...r.kernel.org>,
	Kumar Gala <galak@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Laxman Dewangan <ldewangan@...dia.com>
Subject: Re: [PATCH v4] extcon: gpio: Add the support for Device tree bindings

On Tue, May 31, 2016 at 2:35 AM, Chanwoo Choi <cw00.choi@...sung.com> wrote:
> 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

There is a big difference in that each gpio-key is independent. The
only state is pressed or not. A USB connector has multiple pieces of
state information. You may be treating them independently, but I don't
think they should be.

> 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>;'

This is state information about what is currently attached. The
analogy with gpio-keys would be multiple key codes on one gpio which
would be broken...

>
>         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.

So? Different h/w needs different compatible strings.

But again, you are mixing describing the connector (only what is
soldered on a board) and state information (what is attached). Do not
put state information into DT (describe the gpio signals or chip that
provides the state information).

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

This use of DT is just broken. Come up with another way.

Rob