[RFC] PPC: MPIC: necessary readback after EOI?

[Benjamin Herrenschmidt]

On Mon, 2015-01-05 at 12:10 -0600, Scott Wood wrote:
> It would have been nice if a code comment explained why it was doing the
> readback...  I don't see any particular need to wait for EOI completion
> here (unlike when masking).

The EOI is what causes the MPIC to drop it's EE output to the CPU, if the
EOI is processed too slowly & asynchronously (posted write + 33Mhz MPIC)
we observe cases of spurrious interrupts. We had some macs basically getting
a spurrious irq for every MPIC interrupts...

Cheers,
Ben.