DMA---dma_map_single流程

#define dma_map_single(d, a, s, r) dma_map_single_attrs(d, a, s, r, NULL)

  -->

static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
           size_t size,
           enum dma_data_direction dir,
           struct dma_attrs *attrs)
{
 struct dma_map_ops *ops = get_dma_ops(dev); //获取dma_ops
 dma_addr_t addr;

 kmemcheck_mark_initialized(ptr, size);
 BUG_ON(!valid_dma_direction(dir));
 addr = ops->map_page(dev, virt_to_page(ptr), //调用dma_ops的map_page接口
        (unsigned long)ptr & ~PAGE_MASK, size,
        dir, attrs);
 debug_dma_map_page(dev, virt_to_page(ptr),
      (unsigned long)ptr & ~PAGE_MASK, size,
      dir, addr, true);
 return addr;
}

dma_ops的初始化
fs_initcall(pci_iommu_init);  -->

pci_iommu_init(){
...
intel_iommu_init();//设置intel的iommu，如果存在硬件设备的话，设置dma_ops=intel_dma_ops
amd_iommu_init();//设置amd的iommu，如果存在硬件设备的话，设置dma_ops=amd_dma_ops
no_iommu_init();//当不存在iommu设备时，设置dma_ops=nommu_dma_ops
...
}

nommu_map_page最后将地址转换为总线地址，此时的总线地址==CPU域物理地址

static dma_addr_t nommu_map_page(struct device *dev, struct page *page,
     unsigned long offset, size_t size,
     enum dma_data_direction dir,
     struct dma_attrs *attrs)
{
 dma_addr_t bus = page_to_phys(page) + offset; //总线地址就等于物理地址。
 WARN_ON(size == 0);
 if (!check_addr("map_single", dev, bus, size))
  return bad_dma_address;
 flush_write_buffers();
 return bus;
}