1 /* SPDX-License-Identifier: GPL-2.0-or-later */
6 * Contiguous Memory Allocator for DMA mapping framework
7 * Copyright (c) 2010-2011 by Samsung Electronics.
9 * Marek Szyprowski <m.szyprowski@samsung.com>
10 * Michal Nazarewicz <mina86@mina86.com>
14 * Contiguous Memory Allocator
16 * The Contiguous Memory Allocator (CMA) makes it possible to
17 * allocate big contiguous chunks of memory after the system has
22 * Various devices on embedded systems have no scatter-getter and/or
23 * IO map support and require contiguous blocks of memory to
24 * operate. They include devices such as cameras, hardware video
27 * Such devices often require big memory buffers (a full HD frame
28 * is, for instance, more then 2 mega pixels large, i.e. more than 6
29 * MB of memory), which makes mechanisms such as kmalloc() or
30 * alloc_page() ineffective.
32 * At the same time, a solution where a big memory region is
33 * reserved for a device is suboptimal since often more memory is
34 * reserved then strictly required and, moreover, the memory is
35 * inaccessible to page system even if device drivers don't use it.
37 * CMA tries to solve this issue by operating on memory regions
38 * where only movable pages can be allocated from. This way, kernel
39 * can use the memory for pagecache and when device driver requests
40 * it, allocated pages can be migrated.
44 * CMA should not be used by the device drivers directly. It is
45 * only a helper framework for dma-mapping subsystem.
47 * For more information, see kernel-docs in kernel/dma/contiguous.c
52 #include <linux/device.h>
59 extern struct cma *dma_contiguous_default_area;
61 static inline struct cma *dev_get_cma_area(struct device *dev)
63 if (dev && dev->cma_area)
65 return dma_contiguous_default_area;
68 static inline void dev_set_cma_area(struct device *dev, struct cma *cma)
74 static inline void dma_contiguous_set_default(struct cma *cma)
76 dma_contiguous_default_area = cma;
79 void dma_contiguous_reserve(phys_addr_t addr_limit);
81 int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base,
82 phys_addr_t limit, struct cma **res_cma,
86 * dma_declare_contiguous() - reserve area for contiguous memory handling
87 * for particular device
88 * @dev: Pointer to device structure.
89 * @size: Size of the reserved memory.
90 * @base: Start address of the reserved memory (optional, 0 for any).
91 * @limit: End address of the reserved memory (optional, 0 for any).
93 * This function reserves memory for specified device. It should be
94 * called by board specific code when early allocator (memblock or bootmem)
98 static inline int dma_declare_contiguous(struct device *dev, phys_addr_t size,
99 phys_addr_t base, phys_addr_t limit)
103 ret = dma_contiguous_reserve_area(size, base, limit, &cma, true);
105 dev_set_cma_area(dev, cma);
110 struct page *dma_alloc_from_contiguous(struct device *dev, size_t count,
111 unsigned int order, bool no_warn);
112 bool dma_release_from_contiguous(struct device *dev, struct page *pages,
117 static inline struct cma *dev_get_cma_area(struct device *dev)
122 static inline void dev_set_cma_area(struct device *dev, struct cma *cma) { }
124 static inline void dma_contiguous_set_default(struct cma *cma) { }
126 static inline void dma_contiguous_reserve(phys_addr_t limit) { }
128 static inline int dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base,
129 phys_addr_t limit, struct cma **res_cma,
136 int dma_declare_contiguous(struct device *dev, phys_addr_t size,
137 phys_addr_t base, phys_addr_t limit)
143 struct page *dma_alloc_from_contiguous(struct device *dev, size_t count,
144 unsigned int order, bool no_warn)
150 bool dma_release_from_contiguous(struct device *dev, struct page *pages,