linux-kernel - Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq demuxer chip

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Message-ID: <20150210165201.634bc04b@bbrezillon>
Date:	Tue, 10 Feb 2015 16:52:01 +0100
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq
 demuxer chip

Hi Mark,

On Tue, 10 Feb 2015 15:36:28 +0000
Mark Rutland <mark.rutland@....com> wrote:

> Hi Boris,
> 
> On Thu, Jan 29, 2015 at 10:33:38AM +0000, Boris Brezillon wrote:
> > Add documentation for the virtual irq demuxer.
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> > Acked-by: Nicolas Ferre <nicolas.ferre@...el.com>
> > ---
> >  .../bindings/interrupt-controller/dumb-demux.txt   | 41 ++++++++++++++++++++++
> >  1 file changed, 41 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt b/Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt
> > new file mode 100644
> > index 0000000..b9a7830
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt
> > @@ -0,0 +1,41 @@
> > +* Virtual Interrupt Demultiplexer
> > +
> > +This virtual demultiplexer simply forward all incoming interrupts to its
> > +enabled/unmasked children.
> > +It is only intended to be used by hardware that do not provide a proper way
> > +to demultiplex a source interrupt, and thus have to wake all their children
> > +up so that they can possibly handle the interrupt (if needed).
> > +This can be seen as an alternative to shared interrupts when at least one
> > +of the interrupt children is a timer (and require the irq to stay enabled
> > +on suspend) while others are not. This will prevent calling irq handlers of
> > +non timer devices while they are suspended.
> 
> This sounds like a DT-workaround for a Linux implementation problem, and
> I don't think this the right way to solve your problem.

I understand your concern, but why are you answering while I asked for
DT maintainers reviews for several days (if not several weeks).

> 
> Why does this have to be in DT at all? Why can we not fix the core to
> handle these details?

We already discussed that with Rob and Thomas, and hiding such a
demuxer chip is not an easy task.
I'm open to any suggestion to do that, though I'd like you (I mean DT
guys) to provide a working implementation (or at least a viable concept)
that would silently demultiplex an irq.

> 
> I am very much not keen on this binding.

Yes, but do you have anything else to propose.
We're experiencing this warning for 2 releases now, and this is time to
find a solution (even if it's not a perfect one).

> 
> > +
> > +Required properties:
> > +- compatible: Should be "virtual,irq-demux".
> > +- interrupt-controller: Identifies the node as an interrupt controller.
> > +- interrupts-extended or interrupt-parent and interrupts: Reference the source
> > +  interrupt connected to this dumb demuxer.
> > +- #interrupt-cells: The number of cells to define the interrupts (should be 1).
> > +  The only cell is the IRQ number.
> > +- irqs: u32 bitfield specifying the interrupts provided by the demuxer.
> 
> Arbitrary limitation?

I first proposed to make this field unlimited, but Thomas suggested to
keep it limited to 32 bits (and I didn't complain since my HW needs
far less than 32 interrupts).

Best Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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