[PATCH 1/4] dma: define __dma_aligned attribute

Ahmad Fatoum a.fatoum at pengutronix.de
Thu Sep 21 02:56:46 PDT 2023

Unlike the kernel, we always map barebox stack 1:1, so DMA to barebox
stack is ok if care is taken for alignment. Otherwise, cache maintenance
may end up clobbering data unintentionally.

Provide a __dma_aligned attribute for use in such situations and use the
already existing DMA_ALIGNMENT as alignment.

To be able to do that, we need to make sure that the default DMA_ALIGNMENT
is only defined when architectures don't define their own dma_alloc. If
they do, they are responsible to define their own DMA_ALIGNMENT as well.

The new attribute is intentionally not called __cacheline_aligned,
because it differs functionally: We care about the cache line size of
the outer cache, while in Linux __cacheline_aligned is for L1 cache.
A __dma_aligned wouldn't make sense for Linux as it would be too easy to
abuse (e.g. placing it on VMAP_STACK), but for barebox, we do this at
many places and an attribute would increase readability and even safety.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
 include/dma.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/dma.h b/include/dma.h
index 2a09b747d1e2..469c482e7a3a 100644
--- a/include/dma.h
+++ b/include/dma.h
@@ -17,17 +17,19 @@
+#ifndef dma_alloc
 #define DMA_ALIGNMENT	32
-#ifndef dma_alloc
 static inline void *dma_alloc(size_t size)
 	return xmemalign(DMA_ALIGNMENT, ALIGN(size, DMA_ALIGNMENT));
+#define __dma_aligned __attribute__((__aligned__((DMA_ALIGNMENT))))
 #ifndef dma_free
 static inline void dma_free(void *mem)

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