linux-kernel - Re: [PATCH] RFC: interrupt consistency check for OF GPIO IRQs

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Message-ID: <20131020155135.GW12599@atomide.com>
Date:	Sun, 20 Oct 2013 08:51:35 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Grant Likely <grant.likely@...aro.org>,
	Alexander Holler <holler@...oftware.de>,
	Stephen Warren <swarren@...dotorg.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux-OMAP <linux-omap@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Enric Balletbo i Serra <eballetbo@...il.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Kevin Hilman <khilman@...aro.org>,
	Balaji T K <balajitk@...com>,
	Jon Hunter <jgchunter@...il.com>
Subject: Re: [PATCH] RFC: interrupt consistency check for OF GPIO IRQs

* Laurent Pinchart <laurent.pinchart@...asonboard.com> [131020 05:41]:
> Hi Grant,
> 
> On Tuesday 17 September 2013 17:36:32 Grant Likely wrote:
> > On Thu, 12 Sep 2013 17:57:00 +0200, Alexander Holler wrote:
> > > Am 12.09.2013 17:19, schrieb Stephen Warren:
> > > > IRQs, DMA channels, and GPIOs are all different things. Their bindings
> > > > are defined independently. While it's good to define new types of
> > > > bindings consistently with other bindings, this hasn't always happened,
> > > > so you can make zero assumptions about the IRQ bindings by reading the
> > > > documentation for any other kind of binding.
> > > > 
> > > > Multiple interrupts are defined as follows:
> > > > 	// Optional; otherwise inherited from parent/grand-parent/...
> > > > 	interrupt-parent = <&gpio6>;
> > > > 	// Must be in a fixed order, unless binding defines that the
> > > > 	// optional interrupt-names property is to be used.
> > > > 	interrupts = <1 IRQF_TRIGGER_HIGH> <2 IRQF_TRIGGER_LOW>;
> > > > 	// Optional; binding for device defines whether it must
> > > > 	// be present
> > > > 	interrupt-names = "foo", "bar";
> > > > 
> > > > If you need multiple interrupts, each with a different parent, you need
> > > > to use an interrupt-map property (Google it for a more complete
> > > > explanation I guess). Unlike "interrupts", "interrupt-map" has a phandle
> > > > in each entry, and hence each entry can refer to a different IRQ
> > > > controller. You end up defining a dummy interrupt controller node (which
> > > > may be the leaf node with multiple IRQ outputs, which then points at
> > > > itself as the interrupt parent), pointing the leaf node's
> > > > interrupt-parent at that node, and then having interrupt-map "demux" the
> > > > N interrupt outputs to the various interrupt controllers.
> > > 
> > > What a mess. I assume that is the price that bindings don't have to
> > > change.
> > > 
> > > Thanks for clarifying that,
> > > 
> > > Alexander Holler
> > 
> > Actually, I think it is solveable but doing so requires a new binding
> > for interrupts. I took a shot at implementing it earlier this week and
> > I've got working patches that I'll be posting soon. I created a new
> > "interrupts-extended" property that uses a phandle+args type of
> > binding like this:
> > 
> > intc1: intc@...0 {
> > 	interrupt-controller;
> > 	#interrupt-cells = <1>;
> > };
> > 
> > intc2: intc@...0 {
> > 	interrupt-controller;
> > 	#interrupt-cells = <2>;
> > };
> > 
> > device@...0 {
> > 	interrupts-extended = <&intc1 5> <&intc2 3 4> <&intc1 6>;
> > };
> > 
> > 'interrupts-extended' will be proposed as a directly replacement of the
> > 'interrupts' property and it will eliminate the need for an
> > interrupt-map property. A node will be allowed to have one or the other,
> > but not both.
> > 
> > I'll write up a proper binding document and post for review.
> 
> Any progress on this ? I'll need to use multiple interrupts with different 
> parents in the near future, I can take this over if needed.

Grant posted the interrupts-extended binding few days ago:

http://lkml.org/lkml/2013/10/15/760
 
> I've also been thinking that we could possibly reuse the "interrupts" property 
> without defining a new "interrupts-extended". When parsing the property the 
> code would use the current DT bindings if an interrupt-parent is present, and 
> the new DT bindings if it isn't.

That could lead to mysterious failures easily as the binding
behaves in two different ways :) Probably best to have a separate
binding for it.

Regards,

Tony

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