include/linux/dma-contiguous.h

   1 #ifndef __LINUX_CMA_H
   2 #define __LINUX_CMA_H
   3
   4 /*
   5  * Contiguous Memory Allocator for DMA mapping framework
   6  * Copyright (c) 2010-2011 by Samsung Electronics.
   7  * Written by:
   8  *      Marek Szyprowski <m.szyprowski@samsung.com>
   9  *      Michal Nazarewicz <mina86@mina86.com>
  10  *
  11  * This program is free software; you can redistribute it and/or
  12  * modify it under the terms of the GNU General Public License as
  13  * published by the Free Software Foundation; either version 2 of the
  14  * License or (at your optional) any later version of the license.
  15  */
  16
  17 /*
  18  * Contiguous Memory Allocator
  19  *
  20  *   The Contiguous Memory Allocator (CMA) makes it possible to
  21  *   allocate big contiguous chunks of memory after the system has
  22  *   booted.
  23  *
  24  * Why is it needed?
  25  *
  26  *   Various devices on embedded systems have no scatter-getter and/or
  27  *   IO map support and require contiguous blocks of memory to
  28  *   operate.  They include devices such as cameras, hardware video
  29  *   coders, etc.
  30  *
  31  *   Such devices often require big memory buffers (a full HD frame
  32  *   is, for instance, more then 2 mega pixels large, i.e. more than 6
  33  *   MB of memory), which makes mechanisms such as kmalloc() or
  34  *   alloc_page() ineffective.
  35  *
  36  *   At the same time, a solution where a big memory region is
  37  *   reserved for a device is suboptimal since often more memory is
  38  *   reserved then strictly required and, moreover, the memory is
  39  *   inaccessible to page system even if device drivers don't use it.
  40  *
  41  *   CMA tries to solve this issue by operating on memory regions
  42  *   where only movable pages can be allocated from.  This way, kernel
  43  *   can use the memory for pagecache and when device driver requests
  44  *   it, allocated pages can be migrated.
  45  *
  46  * Driver usage
  47  *
  48  *   CMA should not be used by the device drivers directly. It is
  49  *   only a helper framework for dma-mapping subsystem.
  50  *
  51  *   For more information, see kernel-docs in drivers/base/dma-contiguous.c
  52  */
  53
  54 #ifdef __KERNEL__
  55
  56 struct cma;
  57 struct page;
  58 struct device;
  59
  60 #ifdef CONFIG_CMA
  61
  62 /*
  63  * There is always at least global CMA area and a few optional device
  64  * private areas configured in kernel .config.
  65  */
  66 #define MAX_CMA_AREAS   (1 + CONFIG_CMA_AREAS)
  67
  68 extern struct cma *dma_contiguous_default_area;
  69
  70 void dma_contiguous_reserve(phys_addr_t addr_limit);
  71 int dma_declare_contiguous(struct device *dev, phys_addr_t size,
  72                            phys_addr_t base, phys_addr_t limit);
  73
  74 struct page *dma_alloc_from_contiguous(struct device *dev, int count,
  75                                        unsigned int order);
  76 bool dma_release_from_contiguous(struct device *dev, struct page *pages,
  77                                  int count);
  78
  79 #else
  80
  81 #define MAX_CMA_AREAS   (0)
  82
  83 static inline void dma_contiguous_reserve(phys_addr_t limit) { }
  84
  85 static inline
  86 int dma_declare_contiguous(struct device *dev, phys_addr_t size,
  87                            phys_addr_t base, phys_addr_t limit)
  88 {
  89         return -ENOSYS;
  90 }
  91
  92 static inline
  93 struct page *dma_alloc_from_contiguous(struct device *dev, int count,
  94                                        unsigned int order)
  95 {
  96         return NULL;
  97 }
  98
  99 static inline
 100 bool dma_release_from_contiguous(struct device *dev, struct page *pages,
 101                                  int count)
 102 {
 103         return false;
 104 }
 105
 106 #endif
 107
 108 #endif
 109
 110 #endif