[NEWBIE] Interrupt-problem mpc5200

Matt Sealey matt at genesi-usa.com
Fri Sep 14 23:29:59 EST 2007


I have a newbie question which I never had properly answered. On the
MPC52xx and specifically regarding the device tree, how are interrupt
numbers assigned?

On Efika (and in the DT docs) it's basically the X Y Z where X is the
type (critical, main, peripheral, sdma), Y is the number of the
interrupt, and Z is it's sense level.

However while X and Z are easy to derive, how do you work out what Y
is meant to be given a device? Is it a bit number in the interrupt
register, or the value of the encoded interrupt register or something
else algorithmically determined?

I am just finding the code in Linux that derives this number fairly
elusive (the irq setup function for the mpc52xx platform is truly
sparse, irq_of_find_and_map isn't much help). Maybe I am just not
looking in the right place but not being an MPC52xx PIC Expert I
wouldn't even know where to start...

Matt Sealey <matt at genesi-usa.com>
Genesi, Manager, Developer Relations

Grant Likely wrote:
> On 9/11/07, S. Fricke <silvio.fricke at googlemail.com> wrote:
>> Hello,
>>>> [...]
>>>>     intr = mpc52xx_find_and_map("mpc52xx-pic");
>>>>     if(!intr) {
>>>>         panic(__FILE__ ": mpc52xx-pic - MAP failed");
>>>>     }
>>>>     set_irq_chip(MPC52xx_IRQ2, &my_irq_chip);
>>> You probably don't want to do this (unless you are cascading IRQs to
>>> custom external hardware).  All you should need is the call to
>>> request_irq() to register your irq handler, and code in your ISR
>>> handler to clear the interrupt condition.
>>> You do *NOT* want to program the interrupt controller directly.  The
>>> mpc5200 interrupt controller already has a driver.  Don't go twiddling
>>> the registers manually.
>> OK!
>> I have tried it before and i get a "-ENOSYS" returned.
>> My code was/is now:
>> --==>
>> request_irq(MPC52xx_IRQ2, intmod_isr, IRQF_DISABLED , "intmod",
>>             INTMOD_IRQ_BOARD);
>> <==--
>> I have looked up "kernel/irq/manage.c". "-ENOSYS" is returned on function
>> "setup_irq" because the used irq(MPC52xx_IRQ2) is the same as no_irq_chip.
>> THE MPC52xx_IRQ2 is a excerpt from "include/ppc/mpc52xx.h" (per copy
>> paste), but mpc52xx is (now) a powerpc-arch. What is the desired value for
>> IRQ-2 on a mpc5200b?
> The irq number you pass into request_irq is a system-wide irq number;
> it doesn't necessarily map directly onto the MPC52xx irq number.
> Typically, you'd have a node for your device in the device tree which
> has a phandle back to the interrupt node and you would use
> irq_of_parse_and_map() to map it back to a system-wide irq number.
> Otherwise, you need to call of_irq_map_raw with the pointer to the
> 52xx interrupt controller node and the interrupt number in the form
> expected by the device tree.  (But adding a device tree node for your
> device is far easier).
> Cheers,
> g.

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