Open Firmware and interrupt trigger

Benjamin Herrenschmidt benh at
Fri Feb 25 07:46:58 EST 2011

On Wed, 2011-02-23 at 22:18 +0100, Robert Thorhuus wrote:
> Hello!
> I'm quite new to linux and Open Firmware.
> I have a PPC processor. To this I have a Compact Flash connected. The Compact Flash is using external interrupt 0 of the processor.
> In my DTS file I have specified a Compact Flash node and within it I have an interrupt element:
> interrupt = <0 2 0 0>;
> Here I thought the first number was the ID of the interrupt and the second one should be a number indicating how the interrupt is triggered (high, low, raising, falling).
> The interrupt is active low.
> But I could not get it to work which ever value I chose.
> Looking in the code I found this in function __devinit pata_of_platform_probe in file pata_of_platform.c:
> 	ret = of_irq_to_resource(dn, 0, &irq_res);
> 	if (ret == NO_IRQ)
> 		irq_res.start = irq_res.end = 0;
> 	else
> 		irq_res.flags = 0;
> Here "flags" will be zero whatever I do in the DTS. As far as I can understand the flags are defined in interrupts.h:
> #define IRQF_TRIGGER_NONE       0x00000000
> #define IRQF_TRIGGER_RISING     0x00000001
> #define IRQF_TRIGGER_FALLING    0x00000002
> #define IRQF_TRIGGER_HIGH       0x00000004
> #define IRQF_TRIGGER_LOW        0x00000008

Actually, the .dts flags depend on the specific interrupt controller you
are using. For example, MPIC uses a different mapping scheme (for
historical reasons). Check booting-without-of.txt.

> So modifying the code to:
> 	else
> 		irq_res.flags = 2;
> I get it to work.
> Could someone please explain to me why the "flags" parameter is hardcoded zero or just point in a good direction.

That does indeed look odd. Might be worth trying to figure out with the
git history who came up with that code in the first place and ask that
person. Without answer, I think it's valid to patch that out.


> Thank you
> BR
> Robert
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