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>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
index ba4ec39a1131..57b5c3c82e86 100644
--- a/include/asm-generic/cacheflush.h
+++ b/include/asm-generic/cacheflush.h
@@ -13,6 +13,7 @@
 #define flush_cache_dup_mm(mm)                  do { } while (0)
 #define flush_cache_range(vma, start, end)      do { } while (0)
 #define flush_cache_page(vma, vmaddr, pfn)      do { } while (0)
+#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)