64bit DMA on 32bit CPU
sg列表中使用dma_addr_t，
struct scatterlist {
#ifdef CONFIG_DEBUG_SG
unsigned long sg_magic;
#endif
unsigned long page_link;
unsigned int offset;
unsigned int length;
dma_addr_t dma_address;
#ifdef CONFIG_NEED_SG_DMA_LENGTH
unsigned int dma_length;
#endif
};
dma_addr_t定義，
#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
typedef u64 dma_addr_t;
#else
typedef u32 dma_addr_t;
#endif /* dma_addr_t */
CONFIG_ARCH_DMA_ADDR_T_64BIT在下面文件中使用，
---- ARCH_DMA_ADDR_T_64BIT Matches (5 in 4 files) ----
bus.c (drivers\pci) line 101 : #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
pci_bus_alloc_resource in bus.c (drivers\pci) : #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
tegra_cursor_plane_update in dc.c (drivers\gpu\drm\tegra) : #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
starfire.c (drivers\net\ethernet\adaptec) line 139 : #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
types.h (include\linux) line 146 : #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT