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Date:   Mon, 18 Sep 2017 12:22:28 +0800
From:   Huacai Chen <>
To:     Andrew Morton <>
Cc:     Fuxin Zhang <>,,, Huacai Chen <>,
Subject: [PATCH V5 2/3] mm: dmapool: Align to ARCH_DMA_MINALIGN in non-coherent DMA mode

In non-coherent DMA mode, kernel uses cache flushing operations to
maintain I/O coherency, so the dmapool objects should be aligned to
ARCH_DMA_MINALIGN. Otherwise, it will cause data corruption, at least
on MIPS:

	Step 1, dma_map_single
	Step 2, cache_invalidate (no writeback)
	Step 3, dma_from_device
	Step 4, dma_unmap_single

If a DMA buffer and a kernel structure share a same cache line, and if
the kernel structure has dirty data, cache_invalidate (no writeback)
will cause data lost.

Signed-off-by: Huacai Chen <>
 mm/dmapool.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/dmapool.c b/mm/dmapool.c
index 4d90a64..6263905 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -140,6 +140,9 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
 	else if (align & (align - 1))
 		return NULL;
+	if (!device_is_coherent(dev))
+		align = max_t(size_t, align, dma_get_cache_alignment());
 	if (size == 0)
 		return NULL;
 	else if (size < 4)

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