The attr field

The attr field can have the following bits:

#define AS_ATTR_READABLE 0x0001
Address range is readable.
#define AS_ATTR_WRITABLE 0x0002
Address range is writable.
#define AS_ATTR_CACHABLE 0x0004
Address range can be cached (this bit should be off if you're using device memory).
#define AS_ATTR_KIDS 0x0010
Indicates that there are other entries that use this one as their owner. Note that the library turns on this bit automatically; you shouldn't specify it when creating the section.
#define AS_ATTR_CONTINUED 0x0020
Indicates that there are multiple entries being used to describe one "logical" address range. This bit will be on in all but the last one. Note that the library turns on this bit and uses it internally; you shouldn't specify it when creating the section.