@@ -40,6 +40,8 @@ Buffer Requirements:
- If the buffer is not cache-line aligned invalidation will be restricted
to the aligned part. That is, one cache-line at the respective boundary
may be left out while doing invalidation.
+- A suitable buffer can be alloced on the stack using the
+ ALLOC_CACHE_ALIGN_BUFFER macro.
Cleanup Before Linux:
- cleanup_before_linux() should flush the D-cache, invalidate I-cache, and
@@ -822,6 +822,64 @@ int cpu_release(int nr, int argc, char * const argv);
+ * The ALLOC_CACHE_ALIGN_BUFFER macro is used to allocate a buffer on the
+ * stack that meets the minimum architecture alignment requirements for DMA.
+ * Such a buffer is useful for DMA operations where flushing and invalidating
+ * the cache before and after a read and/or write operation is required for
+ * correct operations.
+ * When called the macro creates an array on the stack that is sized such
+ * that:
+ * 1) The beginning of the array can be advanced enough to be aligned.
+ * 2) The size of the aligned portion of the array is a multiple of the minimum
+ * architecture alignment required for DMA.
+ * 3) The aligned portion contains enough space for the original number of
+ * elements requested.
+ * The macro then creates a pointer to the aligned portion of this array and
+ * assigns to the pointer the address of the first element in the aligned
+ * portion of the array.
+ * Calling the macro as:
+ * ALLOC_CACHE_ALIGN_BUFFER(uint32_t, buffer, 1024);
+ * Will result in something similar to saying:
+ * uint32_t buffer;
+ * The following differences exist:
+ * 1) The resulting buffer is guaranteed to be aligned to the value of
+ * ARCH_DMA_MINALIGN.
+ * 2) The buffer variable created by the macro is a pointer to the specified
+ * type, and NOT an array of the specified type. This can be very important
+ * if you want the address of the buffer, which you probably do, to pass it
+ * to the DMA hardware. The value of &buffer is different in the two cases.
+ * In the macro case it will be the address of the pointer, not the address
+ * of the space reserved for the buffer. However, in the second case it
+ * would be the address of the buffer. So if you are replacing hard coded
+ * stack buffers with this macro you need to make sure you remove the & from
+ * the locations where you are taking the address of the buffer.
+ * Note that the size parameter is the number of array elements to allocate,
+ * not the number of bytes.
+ * This macro can not be used outside of function scope, or for the creation
+ * of a function scoped static buffer. It can not be used to create a cache
+ * line aligned global buffer.
+#define ALLOC_CACHE_ALIGN_BUFFER(type, name, size) \
+ char __##name[ROUND(size * sizeof(type), ARCH_DMA_MINALIGN) + \
+ ARCH_DMA_MINALIGN - 1]; \
+ type *name = (type *) ALIGN((uintptr_t)__##name, ARCH_DMA_MINALIGN)
/* Pull in stuff for the build system */
# include <environment.h>