irq_disable() not working

[Wolfgang Grandegger]

Hello,

I'm trying to understand how irq_disable() is supposed to work on
PowerPC systems. Most PowerPC PIC do *not* implement the enable and
disable, but just the unmask and mask methods, e.g:

  http://lxr.linux.no/linux+v2.6.26.5/arch/powerpc/sysdev/mpic.c#L867

The irq_disable() function will then call the default function
default_disable():

  http://lxr.linux.no/linux+v2.6.26.5/kernel/irq/chip.c#L234

which does not *nothing*. I do not see how the interrupt gets disabled
on the hardware level. Obviously I have missed something. TIA for
clarification.

Wolfgang.