Does Cortex-A12 not supprt AMBA4 ACE protocol?
The figure and description of the Cortex-A12 product page(http://www.arm.com/products/processors/cortex-a/cortex-a12-processor.php) shows as if it only supports "AMBA4 AXI Bus" is available bus interface.
Compared with AXI4, ACE protocol adds several singals and channels to maintain cache coherent. So it's useless for cache coherent to connect a AXI4 bus master with a cache coherent controller(CCI400). But you can use the ACP port of CA12 to maintain cache coherent.