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

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Date:	Tue, 10 Feb 2015 15:36:28 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Boris Brezillon <boris.brezillon@...e-electrons.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 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.

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

I am very much not keen on this binding.

> +
> +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?

Thanks,
Mark.
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