linux/include/linux/dma-contiguous.h
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   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
  56struct cma;
  57struct page;
  58struct 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
  68extern struct cma *dma_contiguous_default_area;
  69
  70void dma_contiguous_reserve(phys_addr_t addr_limit);
  71int dma_declare_contiguous(struct device *dev, unsigned long size,
  72                           phys_addr_t base, phys_addr_t limit);
  73
  74struct page *dma_alloc_from_contiguous(struct device *dev, int count,
  75                                       unsigned int order);
  76bool dma_release_from_contiguous(struct device *dev, struct page *pages,
  77                                 int count);
  78
  79#else
  80
  81#define MAX_CMA_AREAS   (0)
  82
  83static inline void dma_contiguous_reserve(phys_addr_t limit) { }
  84
  85static inline
  86int dma_declare_contiguous(struct device *dev, unsigned long size,
  87                           phys_addr_t base, phys_addr_t limit)
  88{
  89        return -ENOSYS;
  90}
  91
  92static inline
  93struct page *dma_alloc_from_contiguous(struct device *dev, int count,
  94                                       unsigned int order)
  95{
  96        return NULL;
  97}
  98
  99static inline
 100bool 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
 111
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