block: add helpers to run flush_dcache_page() against a bio and a request's pages

Mtdblock driver doesn't call flush_dcache_page for pages in request.  So,
this causes problems on architectures where the icache doesn't fill from
the dcache or with dcache aliases.  The patch fixes this.

The ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE symbol was introduced to avoid
pointless empty cache-thrashing loops on architectures for which
flush_dcache_page() is a no-op.  Every architecture was provided with this
flush pages on architectires where ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE is
equal 1 or do nothing otherwise.

See "fix mtd_blkdevs problem with caches on some architectures" discussion
on LKML for more information.

Signed-off-by: Ilya Loginov <isloginov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Peter Horton <phorton@bitbox.co.uk>
Cc: "Ed L. Cashin" <ecashin@coraid.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

2 files changed, 2 insertions, 0 deletions

diff --git a/arch/m68k/include/asm/cacheflush_mm.h b/arch/m68k/include/asm/cacheflush_mm.h
index 16bf375fdbe1..73de7c89d8e0 100644
--- a/arch/m68k/include/asm/cacheflush_mm.h
+++ b/arch/m68k/include/asm/cacheflush_mm.h
@@ -128,6 +128,7 @@ static inline void __flush_page_to_ram(void *vaddr)
         }
 }
 
+#define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 1
 #define flush_dcache_page(page)         __flush_page_to_ram(page_address(page))
 #define flush_dcache_mmap_lock(mapping)         do { } while (0)
 #define flush_dcache_mmap_unlock(mapping)       do { } while (0)
diff --git a/arch/m68k/include/asm/cacheflush_no.h b/arch/m68k/include/asm/cacheflush_no.h
index c65f00a94553..89f195656be7 100644
--- a/arch/m68k/include/asm/cacheflush_no.h
+++ b/arch/m68k/include/asm/cacheflush_no.h
@@ -12,6 +12,7 @@
 #define flush_cache_range(vma, start, end)      __flush_cache_all()
 #define flush_cache_page(vma, vmaddr)           do { } while (0)
 #define flush_dcache_range(start,len)           __flush_cache_all()
+#define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 0
 #define flush_dcache_page(page)                 do { } while (0)
 #define flush_dcache_mmap_lock(mapping)         do { } while (0)
 #define flush_dcache_mmap_unlock(mapping)       do { } while (0)