csky: Fixup dma_alloc_coherent with PAGE_SO attribute

This bug is from commit: 2b070ccdf8c0 (fixup abiv2 mmap(... O_SYNC)
failed). In that patch we remove the _PAGE_SO for memory noncache
mapping and this will cause problem when drivers use dma descriptors
to control the transcations without dma_w/rmb().

After referencing other archs' implementation, pgprot_writecombine is
introduced for mmap(... O_SYNC).

Signed-off-by: Guo Ren <ren_guo@c-sky.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/csky/include/asm/pgtable.h b/arch/csky/include/asm/pgtable.h
index c429a6f347de..fc19ba446d62 100644
--- a/arch/csky/include/asm/pgtable.h
+++ b/arch/csky/include/asm/pgtable.h
@@ -258,6 +258,16 @@ static inline pgprot_t pgprot_noncached(pgprot_t _prot)
 {
 	unsigned long prot = pgprot_val(_prot);
 
+	prot = (prot & ~_CACHE_MASK) | _CACHE_UNCACHED | _PAGE_SO;
+
+	return __pgprot(prot);
+}
+
+#define pgprot_writecombine pgprot_writecombine
+static inline pgprot_t pgprot_writecombine(pgprot_t _prot)
+{
+	unsigned long prot = pgprot_val(_prot);
+
 	prot = (prot & ~_CACHE_MASK) | _CACHE_UNCACHED;
 
 	return __pgprot(prot);