The outer cache has a outer_cache_fns.sync function pointer
that can be used to drain the write buffer of the outer cache.
+config CACHE_B15_RAC
+ bool "Enable the Broadcom Brahma-B15 read-ahead cache controller"
+ depends on ARCH_BRCMSTB
+ default y
+ help
+ This option enables the Broadcom Brahma-B15 read-ahead cache
+ controller. If disabled, the read-ahead cache remains off.
+
config CACHE_FEROCEON_L2
bool "Enable the Feroceon L2 cache controller"
depends on ARCH_MV78XX0 || ARCH_MVEBU