Commit 46a6d51c authored by Anton staaf's avatar Anton staaf Committed by Wolfgang Denk

cache: add ALLOC_CACHE_ALIGN_BUFFER macro

This macro is used to allocate cache line size aligned stack
buffers for use with DMA hardware.
Signed-off-by: 's avatarAnton Staaf <robotboy@chromium.org>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Aneesh V <aneesh@ti.com>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Cc: Wolfgang Denk <wd@denx.de>
parent d47031e6
......@@ -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
......
......@@ -843,6 +843,64 @@ int cpu_release(int nr, int argc, char * const argv[]);
#include <asm/cache.h>
#endif
/*
* 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 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 */
#ifdef DO_DEPS_ONLY
# include <environment.h>
......
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