Open Firmware and interrupt trigger

[Robert Thorhuus]

Thank you Benjamin!

Sorry for not using your qouting schema :(

Benjamin, you are right about the IRQ flags. Those interrupt.h flags seems to differ from my processor reference manual.

None the less. Antov, I saw that the code snippet I refer to below:

> 	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;

, originates from the first version of the file pata_of_platform.c and you are the creator :)
Could you explain the hardcoded ".flags = 0" part? 
Looking amatuer-vise in the code it seems that the only thing one is able to control (through Device Tree) regarding interrupts and pata, is the actual IRQ number. Is this a correct assumption?

Thanks
BR
Robert


-----Original Message-----
From: Benjamin Herrenschmidt [mailto:benh at kernel.crashing.org] 
Sent: den 24 februari 2011 21:47
To: Robert Thorhuus
Cc: linuxppc-dev at lists.ozlabs.org
Subject: Re: Open Firmware and interrupt trigger

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.

Cheers,
Ben.

> Thank you
> 
> BR
> Robert
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