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Subject: Re: [PATCH 2/8] Add uli1575 pci-bridge sector to MPC8641HPCN dts file.
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Date: Sun, 03 Jun 2007 09:51:38 +1000
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> By far the most important registers are the ones at 0x20 since
> you access them at every interrupt. The registers at 0x4d0
> are typically set by firmware and never touched later, there
> is not a single access to them in sysdev/i8259.c.
> 
> I have vague memories of a node named i8259@20 one a board 
> who had OF in 1997 (a Motorola MVME but they switched to 
> PPCBUG just after :-().

Here's the entry for a 8259 in an old pSeries device-tree:

(Note the use of the recommended naming practice where the name is
actually the device-class)

/proc/device-tree/pci@fef00000/isa@b/interrupt-controller@i20:
name             "interrupt-controller"
linux,phandle    00ceed58 (13561176)
interrupt-parent 00c73068 (13054056)
interrupt-controller

#interrupt-cells 00000002
interrupts       00000000 00000002
reserved-interrupts
                 00000002 00000003
reg              00000001 00000020 00000002 00000001
                 000000a0 00000002 00000001 000004d0
                 00000002
compatible       "chrp,iic"
built-in
model            "WINB,W83C553"
device_type      "interrupt-controller"
ibm,loc-code     "P2"