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Re: Interrupt handling and routing: The Big Picture


On Tue, 13 Mar 2012 14:36:00 +0100
Frank Wille <frank%phoenix.owl.de@localhost> wrote:

> > > Maybe newer CPUs with critical interrupts should be handled like in
> > > powerpc/booke/e500_intr.c ?
> > Well. It looks like I can programm the PIC so that it only generates
> > standard interrupts...
> Hm. Really? I had a glance at the interrupt routing diagram in the UM
> yesterday, and it looked like some devices can only deliver critial
> interrupts.

You can always have several exceptions trigger the same PIC and have your 
driver figure out which one it was.

> > Yes. But the hwirq is just an int number. The MPC5200 PIC has four
> > types of interrupts: Peripheral, External, Main and BestComm. All
> > these interrupts are numbered starting at 0. So I have to do some
> > things like: hwirq 0..31 is External, 32..63 is Main, 64..95 is
> > Peripheral, 96..112 is BestComm. At least the OpenFirmWare seems to
> > do something like this. [...]
> Yes. You can use any hwirq number you like. Just your PIC driver needs
> to perform the right actions on it.

Indeed, the hwirq number in this context is nothing but a single number to 
identify an interrupt, it doesn't need to have anything to do with actual 
Jochen - for a simple PIC driver just look at macppc's Heathrow or Ohare ( 
arch/macppc/macppc/pic_heathrow.c and pic_ohare.c ) - the 'interrupt 
controller' there is nothing but a handful bitmapped registers to enable, clear 
and check status on a bunch of interrupt lines.
The reason why the interrupt code looks like this is the fact that there are 
many powerpc boxes with several cascaded interrupt controllers ( examples: the 
powerbook 3400 has two ohares, some ofppc and prep boxes have i8259 cascaded 
with IVRs or OpenPICs and so on ), this way we can set up each one separately 
and then wire them together as needed ( and that's why each one has a number 
range, so the hwirq number is not per pic but per pic tree )

have fun

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