Re: [PATCH v1 1/2] iio:iio-interrupt-trigger: device-tree support

[Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Sun, Feb 21, 2016 at 07:55:24PM +0000, Jonathan Cameron wrote:
> On 19/02/16 19:18, Gregor Boirie wrote:
> > From: Grégor Boirie <gregor.boirie-ITF29qwbsa/QT0dZR+AlfA@public.gmane.org>
> > 
> > Signed-off-by: Gregor Boirie <gregor.boirie-ITF29qwbsa/QT0dZR+AlfA@public.gmane.org>
> Snag here is that iio_interrupt_trigger is a very linux specific
> name and device tree bindings should be just about the hardware.
> 
> Not entirely sure how we avoid this though as the use is rather
> hard to describe generically.
> 
> cc'd device tree list and bindings maintainers.
> 
> As a brief summary - this IIO trigger driver takes a generic
> interrupt (from whatever) and uses it to drive sampling of IIO devices.
> The interrupt might be associated with particularly simple sensors directly
> but is more commonly a gpio interrupt line used cause samples to be captured
> from unrelated devices.  Sometimes the source of that interrupt can be a convoluted
> external mux setup over which linux has no control for example.

If linux has no control of the setup, then do we care? It's just some 
blackbox driving a signal.

> Any suggestions on appropriate naming?

I would think of it outside of IIO perhaps. We already have gpio-keys 
which is kind of similar. Maybe just "external interrupt"? Is it always 
a GPIO interrupt or could be polled GPIO or some other mechanism?

Could you add "trigger-gpios" to every device that uses it and allow for 
it to appear multiple times? It somewhat depends on how static setting 
the trigger source is whether that would be appropriate.

> We aren't really describing hardware here, rather a policy decision on what
> a given interrupt is to be used for.
> 
> I suppose ultimately we could take the view this should be handled via another
> route (from userspace via an appropriate configfs interface for example).

You would still need to know which GPIOs you could use or assign, so I 
think we need something in DT.

Rob