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, 11 insertions, 0 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1cc02972fbe2..e727f6c44c44 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -752,6 +752,17 @@ struct req_iterator {
 #define rq_iter_last(rq, _iter)					\
 		(_iter.bio->bi_next == NULL && _iter.i == _iter.bio->bi_vcnt-1)
 
+#ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+# error	"You should define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE for your platform"
+#endif
+#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+extern void rq_flush_dcache_pages(struct request *rq);
+#else
+static inline void rq_flush_dcache_pages(struct request *rq)
+{
+}
+#endif
+
 extern int blk_register_queue(struct gendisk *disk);
 extern void blk_unregister_queue(struct gendisk *disk);
 extern void register_disk(struct gendisk *dev);