PCI: Add pci_bus_addr_t

[cascardo/linux.git] / include / linux / types.h

diff --git a/include/linux/types.h b/include/linux/types.h
index 59698be..8715287 100644 (file)
--- 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;