diff options
| -rw-r--r-- | arch/sh/mm/cache-sh4.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/arch/sh/mm/cache-sh4.c b/arch/sh/mm/cache-sh4.c index 5cfe08dbb59..7ce81618831 100644 --- a/arch/sh/mm/cache-sh4.c +++ b/arch/sh/mm/cache-sh4.c @@ -581,6 +581,17 @@ static void __flush_cache_4096(unsigned long addr, unsigned long phys, * Break the 1, 2 and 4 way variants of this out into separate functions to * avoid nearly all the overhead of having the conditional stuff in the function * bodies (+ the 1 and 2 way cases avoid saving any registers too). + * + * We want to eliminate unnecessary bus transactions, so this code uses + * a non-obvious technique. + * + * Loop over a cache way sized block of, one cache line at a time. For each + * line, use movca.a to cause the current cache line contents to be written + * back, but without reading anything from main memory. However this has the + * side effect that the cache is now caching that memory location. So follow + * this with a cache invalidate to mark the cache line invalid. And do all + * this with interrupts disabled, to avoid the cache line being accidently + * evicted while it is holding garbage. */ static void __flush_dcache_segment_1way(unsigned long start, unsigned long extent_per_way) |