FIX_FDT
const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
create_fdt_early_page_table(__fix_to_virt(FIX_FDT), dtb_pa);
unsigned long idx = pgd_index(__fix_to_virt(FIX_FDT));
BUILD_BUG_ON(FIX_FDT % (PMD_SIZE / PAGE_SIZE));