linux-kernel - Re: [PATCH 0/5] ARM: at91: fix irq_pm_install

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Date:	Tue, 16 Dec 2014 15:20:41 +0100
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
	Alessandro Zummo <a.zummo@...ertech.it>,
	rtc-linux@...glegroups.com, Mike Turquette <mturquette@...aro.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Andrew Victor <linux@...im.org.za>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] ARM: at91: fix irq_pm_install_action WARNING

On Tue, 16 Dec 2014 13:56:26 +0100 (CET)
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Tue, 16 Dec 2014, Boris Brezillon wrote:
> > Thomas Gleixner <tglx@...utronix.de> wrote:
> > > Install the timer interrupt as a demultiplexing interrupt.
> > 
> > I can try to hack the AIC irqchip driver to implement this demux logic,
> > but this logic can't be placed in the PIT (Periodic Interval Timer)
> > driver itself, because the shared IRQ line is used by the at91 clock
> > controller (PMC) which is providing the clock to the PIT device.
> > This gives the following dependency graph:
> > 
> > PIT =depends-on=> Master Clock =provided-by=> PMC =needs=> PMC IRQ.
> 
> It never can be a part of a device driver. This is a property of the
> interrupt controller which fails to provide a proper demux for this
> irq line in the first place.
> 
> So you fake the demux in the irq chip driver, where you provide the
> pseudo chip and the demux logic. None of the device drivers (PIT, PMC,
> UART ...) even knows about that.
> 
> |--------|             |--------|
> | AIC    |-------------| Pseudo |---- PIT
> |        |             | chip   |---- PMC
> |        |             |        |---- UART
> |        |             |--------|
> |        |--- devX
> |        |--- devY
> |        |--- devZ
> |--------|
> 
> So PIT, PMC and UART get interrupt numbers handed out which are
> outside of the interrupt space of AIC.

Okay, that's what I had in mind, thanks for clarifying this aspect.

Regarding the DT representation, it should look like this, right ?

aic: interrupt-controller@...ff000 {
	#interrupt-cells = <3>;
	compatible = "atmel,at91rm9200-aic";
	interrupt-controller;
	reg = <0xfffff000 0x200>;
	atmel,external-irqs = <29 30 31>;

	irq1_demux: irq1-demux {
		#interrupt-cells = <1>;
		interrupt-controller;
	}
};

pit: timer@...ffd30 {
	compatible = "atmel,at91sam9260-pit";
	reg = <0xfffffd30 0xf>;
	/* 0 is the id reserved for the PIT */
	interrupts-extended = <&irq1_demux 0>;
	clocks = <&mck>;
};

pmc: pmc@...ffc00 {
	compatible = "atmel,at91sam9260-pmc";
	reg = <0xfffffc00 0x100>;
	/* 1 is the id reserved for the PMC */
	interrupts-extended = <&irq1_demux 1>;
[...]
};

Regards,

Boris

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