linux-kernel - Re: How to create IRQ mappings in a GPIO driver that doesn't control its IRQ domain ?

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Date:	Sat, 27 Jul 2013 23:00:21 -0600
From:	Grant Likely <grant.likely@...aro.org>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Mark Brown <broonie@...nel.org>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: How to create IRQ mappings in a GPIO driver that doesn't control its IRQ domain ?

On Thu, 25 Jul 2013 15:22:29 +0200, Laurent Pinchart <laurent.pinchart@...asonboard.com> wrote:
> Hi Mark,
> 
> On Thursday 25 July 2013 14:15:56 Mark Brown wrote:
> > On Thu, Jul 25, 2013 at 11:45:33AM +0200, Laurent Pinchart wrote:
> > > The two devices are independent, so there's no real parent/child
> > > relationship. However, as Grant proposed, I could list all the interrupts
> > > associated with GPIOs in the GPIO controller DT node. I would then just
> > > call irq_of_parse_and_map() in the .to_irq() handler to magically
> > > translate the GPIO number to a mapped IRQ number.
> > > 
> > > The number of interrupts can be pretty high (up to 58 in the worst case so
> > > far), so an alternative would be to specify the interrupt-parent only, and
> > > call irq_create_of_mapping() directly. What solution would you prefer ?
> > 
> > Are the interrupts in a contiguous block in the controller so you can just
> > pass around the controller and a base number?
> 
> In two of the three SoCs I need to fix they are. I've just realized that in 
> the last one the interrupts are in two contiguous blocks in two different 
> parents. I will thus need at least a list of <parent-phandle base count>. Our 
> standard interrupt bindings don't seem to support multiple parents,

You can actually do it by using a dummy node with interrupt-map and
interrupt-map-mask properties, but it is a pretty ugly solution in my
opinion.

> is that 
> something that we want to fix or should I go for custom bindings ?

Yes, I think it is something that we want to fix. Jean-Christophe was
going to propose an alternative to the interrupts property which allows
an array of <phandle interrupt-specifier> tuples, but I've not seen
anything yet. Go ahead and make a proposal.

You could try to encode a base+count variant, but honestly I don't think
it would be a good idea because it only would work with a very narrow
set of use cases. Consider if #interrupt-cells was set to 2. Which cell
gets incremented in the range of interrupts specified? Better I think to
merely have an array of fully specified irqs. Support for that property
could be transparently baked into the core interrupt parsing functions.

g.
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