Why ack interrupt before calling handler?

I am confused by something in ppc_irq_dispatch_handler().  It looks to
me that the interrupt is ack-ed before the handler is called.  Maybe I
am misunderstanding, but doesn't the ack only reset the interrupt
controller?  If so, the interrupting hardware could still be
presenting a level-triggered interrupt.  Wouldn't it make more sense
to let the interrupt routine get service the hardware first, then
reset the interrupt controller?

Thanks,

-kb

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