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

[Guenter Roeck]

On 11/01/2013 04:33 PM, NeilBrown wrote:
> On Fri, 1 Nov 2013 10:16:44 -0700 Mark Rutland <mark.rutland@xxxxxxx> 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@xxxxxxx>
> > >
> > > 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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