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.
Cc: sta...@vger.kernel.org
Signed-off-by: Huacai Chen <che...@lemote.com>
---
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)
--
2.7.0
