linux-kernel - Re: [PATCH] extcon-gpio: add devicetree support.

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Date:	Sat, 02 Nov 2013 23:38:49 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	NeilBrown <neilb@...e.de>, Mark Rutland <mark.rutland@....com>
CC:	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] extcon-gpio: add devicetree support.

On 11/01/2013 04:33 PM, NeilBrown wrote:
> On Fri, 1 Nov 2013 10:16:44 -0700 Mark Rutland <mark.rutland@....com> wrote:
>
>> Hi Neil,
>>
>> While I'm not fundamentally opposed to this binding, I have some issues with
>> its current form and would not want to see this version hit mainline.
>>
>
> Thanks for the review.
>
>> On Fri, Nov 01, 2013 at 09:50:05AM +0000, NeilBrown wrote:
>>>
>>> As this device is not vendor specific, I haven't included any "vendor,"
>>> prefixes.  For my model I used "regulator-gpio" which takes a similar
>>> approach.
>>>
>>> Signed-off-by: NeilBrown <neilb@...e.de>
>>>
>>> diff --git a/Documentation/devicetree/bindings/extcon/extcon-gpio.txt b/Documentation/devicetree/bindings/extcon/extcon-gpio.txt
>>> new file mode 100644
>>> index 000000000000..2346b61cc620
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/extcon/extcon-gpio.txt
>>> @@ -0,0 +1,26 @@
>>> +* EXTCON detector using GPIO
>>
>> EXTCON is _extremely_ Linux-specific. The binding document needs a description
>> of the class of device it's inteded to describe that does not just refer to
>> Linux internals.
>>
>> I would prefer if we could have a better name for this that was not tied to the
>> Linux driver name. Perhaps "gpio-presence-detector"?
>
> Maybe "cable-presence-detector" as in this case the GPIO is just an
> implementation detail.  Which isn't much different from "external-connector"
> which is where "extcon" comes from...
>
> I propose "external-connector" if you don't like "extcon".
>
>
>>
>>> +
>>> +Required Properties:
>>> + - compatible: "extcon-gpio"
>>> + - gpios: gpio line that detects connector
>>> + - interrupts: interrupt generated by that gpio
>>
>> We don't need this. If we need the interrupt a gpio generates, we should ask
>> the gpio controller driver to map the gpio to an interrupt.
>>
>> We have gpiod_to_irq for this in Linux.
>
> The reason I did this was that the pre-existing platform_data wants
> 'irq_flags'.  I could have an 'irq-flags' property, but it seems to make more
> sense to use "interrupts" as that already provides a way to pass irq-flags to
> a device.
>
> On reflection though, I cannot imagine why any extcon-gpio would use anything
> other than  IRQ_TYPE_EDGE_BOTH.  Maybe MyungJoo Ham can explain that???
>
> If there is no need for specifying irq-flags per-platform, the "interrupts"
> property can definitely go.
>

When I tried to add DT support to extcon-pio, I used IRQ_TYPE_EDGE_BOTH.
See [1]. A useful fallback for 'label' - if not specified - may be
np->name, to match LED functionality.

A patch to add 'active low' to the platform data for extcon-gpio is pending
in linux-next. It might make sense to extract this flag from the gpio flags
and add it as well. Again see [1] for an example how this could be implemented.

Guenter

[1] https://lkml.org/lkml/2013/8/30/26

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