+
+void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
+{
+ const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
+ pgprot_t prot = PAGE_KERNEL_RO;
+ int size, offset;
+ void *dt_virt;
+
+ /*
+ * Check whether the physical FDT address is set and meets the minimum
+ * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be
+ * at least 8 bytes so that we can always access the size field of the
+ * FDT header after mapping the first chunk, double check here if that
+ * is indeed the case.
+ */
+ BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
+ if (!dt_phys || dt_phys % MIN_FDT_ALIGN)
+ return NULL;
+
+ /*
+ * Make sure that the FDT region can be mapped without the need to
+ * allocate additional translation table pages, so that it is safe
+ * to call create_mapping() this early.
+ *
+ * On 64k pages, the FDT will be mapped using PTEs, so we need to
+ * be in the same PMD as the rest of the fixmap.
+ * On 4k pages, we'll use section mappings for the FDT so we only
+ * have to be in the same PUD.
+ */
+ BUILD_BUG_ON(dt_virt_base % SZ_2M);
+
+ BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> SWAPPER_TABLE_SHIFT !=
+ __fix_to_virt(FIX_BTMAP_BEGIN) >> SWAPPER_TABLE_SHIFT);
+
+ offset = dt_phys % SWAPPER_BLOCK_SIZE;
+ dt_virt = (void *)dt_virt_base + offset;
+
+ /* map the first chunk so we can read the size from the header */
+ create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
+ SWAPPER_BLOCK_SIZE, prot);
+
+ if (fdt_check_header(dt_virt) != 0)
+ return NULL;
+
+ size = fdt_totalsize(dt_virt);
+ if (size > MAX_FDT_SIZE)
+ return NULL;
+
+ if (offset + size > SWAPPER_BLOCK_SIZE)
+ create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
+ round_up(offset + size, SWAPPER_BLOCK_SIZE), prot);
+
+ memblock_reserve(dt_phys, size);
+
+ return dt_virt;
+}