1 /* SPDX-License-Identifier: GPL-2.0+ */
2 /*
3  * Copyright (c) 2015 Google, Inc
4  */
5 
6 #ifndef __ALIGNMEM_H
7 #define __ALIGNMEM_H
8 
9 /*
10  * ARCH_DMA_MINALIGN is defined in asm/cache.h for each architecture.  It
11  * is used to align DMA buffers.
12  */
13 #ifndef __ASSEMBLY__
14 #include <asm/cache.h>
15 #include <malloc.h>
16 
17 /*
18  * The ALLOC_CACHE_ALIGN_BUFFER macro is used to allocate a buffer on the
19  * stack that meets the minimum architecture alignment requirements for DMA.
20  * Such a buffer is useful for DMA operations where flushing and invalidating
21  * the cache before and after a read and/or write operation is required for
22  * correct operations.
23  *
24  * When called the macro creates an array on the stack that is sized such
25  * that:
26  *
27  * 1) The beginning of the array can be advanced enough to be aligned.
28  *
29  * 2) The size of the aligned portion of the array is a multiple of the minimum
30  *    architecture alignment required for DMA.
31  *
32  * 3) The aligned portion contains enough space for the original number of
33  *    elements requested.
34  *
35  * The macro then creates a pointer to the aligned portion of this array and
36  * assigns to the pointer the address of the first element in the aligned
37  * portion of the array.
38  *
39  * Calling the macro as:
40  *
41  *     ALLOC_CACHE_ALIGN_BUFFER(uint32_t, buffer, 1024);
42  *
43  * Will result in something similar to saying:
44  *
45  *     uint32_t    buffer[1024];
46  *
47  * The following differences exist:
48  *
49  * 1) The resulting buffer is guaranteed to be aligned to the value of
50  *    ARCH_DMA_MINALIGN.
51  *
52  * 2) The buffer variable created by the macro is a pointer to the specified
53  *    type, and NOT an array of the specified type.  This can be very important
54  *    if you want the address of the buffer, which you probably do, to pass it
55  *    to the DMA hardware.  The value of &buffer is different in the two cases.
56  *    In the macro case it will be the address of the pointer, not the address
57  *    of the space reserved for the buffer.  However, in the second case it
58  *    would be the address of the buffer.  So if you are replacing hard coded
59  *    stack buffers with this macro you need to make sure you remove the & from
60  *    the locations where you are taking the address of the buffer.
61  *
62  * Note that the size parameter is the number of array elements to allocate,
63  * not the number of bytes.
64  *
65  * This macro can not be used outside of function scope, or for the creation
66  * of a function scoped static buffer.  It can not be used to create a cache
67  * line aligned global buffer.
68  */
69 #define PAD_COUNT(s, pad) (((s) - 1) / (pad) + 1)
70 #define PAD_SIZE(s, pad) (PAD_COUNT(s, pad) * pad)
71 #define ALLOC_ALIGN_BUFFER_PAD(type, name, size, align, pad)		\
72 	char __##name[ROUND(PAD_SIZE((size) * sizeof(type), pad), align)  \
73 		      + (align - 1)];					\
74 									\
75 	type *name = (type *)ALIGN((uintptr_t)__##name, align)
76 #define ALLOC_ALIGN_BUFFER(type, name, size, align)		\
77 	ALLOC_ALIGN_BUFFER_PAD(type, name, size, align, 1)
78 #define ALLOC_CACHE_ALIGN_BUFFER_PAD(type, name, size, pad)		\
79 	ALLOC_ALIGN_BUFFER_PAD(type, name, size, ARCH_DMA_MINALIGN, pad)
80 #define ALLOC_CACHE_ALIGN_BUFFER(type, name, size)			\
81 	ALLOC_ALIGN_BUFFER(type, name, size, ARCH_DMA_MINALIGN)
82 
83 /*
84  * DEFINE_CACHE_ALIGN_BUFFER() is similar to ALLOC_CACHE_ALIGN_BUFFER, but it's
85  * purpose is to allow allocating aligned buffers outside of function scope.
86  * Usage of this macro shall be avoided or used with extreme care!
87  */
88 #define DEFINE_ALIGN_BUFFER(type, name, size, align)			\
89 	static char __##name[ALIGN(size * sizeof(type), align)]	\
90 			__aligned(align);				\
91 									\
92 	static type *name = (type *)__##name
93 #define DEFINE_CACHE_ALIGN_BUFFER(type, name, size)			\
94 	DEFINE_ALIGN_BUFFER(type, name, size, ARCH_DMA_MINALIGN)
95 
96 /**
97  * malloc_cache_aligned() - allocate a memory region aligned to cache line size
98  *
99  * This allocates memory at a cache-line boundary. The amount allocated may
100  * be larger than requested as it is rounded up to the nearest multiple of the
101  * cache-line size. This ensured that subsequent cache operations on this
102  * memory (flush, invalidate) will not affect subsequently allocated regions.
103  *
104  * @size:	Minimum number of bytes to allocate
105  *
106  * @return pointer to new memory region, or NULL if there is no more memory
107  * available.
108  */
malloc_cache_aligned(size_t size)109 static inline void *malloc_cache_aligned(size_t size)
110 {
111 	return memalign(ARCH_DMA_MINALIGN, ALIGN(size, ARCH_DMA_MINALIGN));
112 }
113 #endif
114 
115 #endif /* __ALIGNMEM_H */
116