location tag

#define HWI_TAG_NAME_location   "location"
#define HWI_TAG_ALIGN_location  (sizeof(uint64))
struct hwi_location {
    struct hwi_prefix   prefix;
    uint32_t            len;
    uint64_t            base;
    uint16_t            regshift;
    uint16_t            addrspace;

Note that location is a simple tag, not an item. It gives the location of the hardware device's registers, whether in a separate I/O space or memory-mapped. There may be more than one of these tags in an item description if there's more than one grouping of registers.

The base field gives the physical address of the start of the registers. The len field gives the length, in bytes, of the registers. The regshift tells how much each register access is shifted by. If a register is documented at offset of a device, then the driver will actually access offset offset2^regshift to get to that register.

The addrspace field is an offset, in bytes, from the start of the asinfo section. It should identify either the memory or io address space item to tell whether the device registers are memory-mapped.