[MiNT] [PATCH][3/5] Add ALLOC_CACHE_ALIGN_BUFFER.

[David Gálvez <dgalvez75@gmail.com>]

Commit message:

Add ALLOC_CACHE_ALIGN_BUFFER macro, this macro allocates memory in the
stack and takes care that the space allocated is cache line size
aligned.
Contributed by David Galvez.

diff -r 1f4685e57172 -r 6b4faecb619c sys/mint/kcompiler.h
--- a/sys/mint/kcompiler.h	Mon Nov 17 11:29:50 2014 +0100
+++ b/sys/mint/kcompiler.h	Mon Nov 17 11:58:16 2014 +0100
@@ -122,4 +122,76 @@
 # define ALIGN(x,a)		__ALIGN_MASK((x),(typeof(x))(a) - 1)
 # define __ALIGN_MASK(x,mask)	(((x) + (mask)) & ~(mask))
 
+/*
+ * This macro is taken from U-Boot - The Universal Boot Loader.
+ * (c) Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ *
+ * 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[1024];
+ *
+ * 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 M68K_CACHE_LINE_SIZE	16
+
+#define PAD_COUNT(s, pad) (((s) - 1) / (pad) + 1)
+#define PAD_SIZE(s, pad) (PAD_COUNT(s, pad) * pad)
+#define ALLOC_ALIGN_BUFFER_PAD(type, name, size, align, pad)		\
+	char __##name[ROUNDUP2(PAD_SIZE((size) * sizeof(type), pad), align)  \
+		      + (align - 1)];					\
+									\
+	type *name = (type *) ALIGN((unsigned long int)__##name, align)
+#define ALLOC_ALIGN_BUFFER(type, name, size, align)		\
+	ALLOC_ALIGN_BUFFER_PAD(type, name, size, align, 1)
+#define ALLOC_CACHE_ALIGN_BUFFER_PAD(type, name, size, pad)		\
+	ALLOC_ALIGN_BUFFER_PAD(type, name, size, M68K_CACHE_LINE_SIZE, pad)
+#define ALLOC_CACHE_ALIGN_BUFFER(type, name, size)			\
+	ALLOC_ALIGN_BUFFER(type, name, size, M68K_CACHE_LINE_SIZE)
+
 # endif /* _mint_misc_h */