MIPS: Loongson-3: Set cache flush handlers to cache_noop

Loongson-3 maintains cache coherency by hardware, this means:
 1) It's icache is coherent with dcache.
 2) It's dcaches don't alias (maybe depend on PAGE_SIZE).
 3) It maintains cache coherency across cores (and for DMA).

So we can skip most cache flush operations by setting relevant handlers
to `cache_noop' in `r4k_cache_init'.
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Steven J . Hill <sjhill@realitydiluted.com>
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12752/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/c-r4k.c

@@ -1796,6 +1796,20 @@ void r4k_cache_init(void)
 		/* Optimization: an L2 flush implicitly flushes the L1 */
 		current_cpu_data.options |= MIPS_CPU_INCLUSIVE_CACHES;
 		break;
+	case CPU_LOONGSON3:
+		/* Loongson-3 maintains cache coherency by hardware */
+		__flush_cache_all	= cache_noop;
+		__flush_cache_vmap	= cache_noop;
+		__flush_cache_vunmap	= cache_noop;
+		__flush_kernel_vmap_range = (void *)cache_noop;
+		flush_cache_mm		= (void *)cache_noop;
+		flush_cache_page	= (void *)cache_noop;
+		flush_cache_range	= (void *)cache_noop;
+		flush_cache_sigtramp	= (void *)cache_noop;
+		flush_icache_all	= (void *)cache_noop;
+		flush_data_cache_page	= (void *)cache_noop;
+		local_flush_data_cache_page	= (void *)cache_noop;
+		break;
 	}
 }