[PATCH V4 5/5] arm: mvebu: Added SMP support for Armada XP

On Tue, Nov 20, 2012 at 05:07:59PM +0000, Thomas Petazzoni wrote:

Dear Will Deacon,

On Tue, 20 Nov 2012 17:01:27 +0000, Will Deacon wrote:

quoted

quoted

I prefer to keep them separate, as we can use coherency without SMP.
That's why I create the coherency_ll.S file instead of putting
everything in this file.

Hmm, can you elaborate a bit more on coherency without SMP please? Do
these controls also affect IO coherency?

The coherency unit does coherency between CPUs, but also between the
CPU and the devices for DMA. So for example the MV78230 is a single-core
variant of the Armada XP, so having CONFIG_SMP for it is useless, but
you still want the CPU to join the coherency fabric in order to provide
coherency with I/O.

Thanks to the coherency unit, we have an almost DMA coherent
architecture (see the HW I/O coherency patches from Gr?gory for
details).

Ok, gotcha -- I didn't realise it was all controlled by the same register on
the CPU side.

Thanks for the explanation,

Will