diff options
Diffstat (limited to 'include/linux/types.h')
| -rw-r--r-- | include/linux/types.h | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/include/linux/types.h b/include/linux/types.h index 59698be03490..8715287c3b1f 100644 --- a/include/linux/types.h +++ b/include/linux/types.h @@ -139,12 +139,20 @@ typedef unsigned long blkcnt_t; */ #define pgoff_t unsigned long -/* A dma_addr_t can hold any valid DMA or bus address for the platform */ +/* + * A dma_addr_t can hold any valid DMA address, i.e., any address returned + * by the DMA API. + * + * If the DMA API only uses 32-bit addresses, dma_addr_t need only be 32 + * bits wide. Bus addresses, e.g., PCI BARs, may be wider than 32 bits, + * but drivers do memory-mapped I/O to ioremapped kernel virtual addresses, + * so they don't care about the size of the actual bus addresses. + */ #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT typedef u64 dma_addr_t; #else typedef u32 dma_addr_t; -#endif /* dma_addr_t */ +#endif typedef unsigned __bitwise__ gfp_t; typedef unsigned __bitwise__ fmode_t; |