1 files changed, 66 insertions, 0 deletions
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 5b8b664422d3..82d3435bf14f 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -21,6 +21,7 @@
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/init.h>
+#include <linux/libfdt.h>
 #include <linux/mman.h>
 #include <linux/nodemask.h>
 #include <linux/memblock.h>
@@ -643,3 +644,68 @@ void __set_fixmap(enum fixed_addresses idx,
 		flush_tlb_kernel_range(addr, addr+PAGE_SIZE);
 	}
 }
+
+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 | PTE_RDONLY;
+	int granularity, 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);
+
+	if (IS_ENABLED(CONFIG_ARM64_64K_PAGES)) {
+		BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> PMD_SHIFT !=
+			     __fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT);
+
+		granularity = PAGE_SIZE;
+	} else {
+		BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> PUD_SHIFT !=
+			     __fix_to_virt(FIX_BTMAP_BEGIN) >> PUD_SHIFT);
+
+		granularity = PMD_SIZE;
+	}
+
+	offset = dt_phys % granularity;
+	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, granularity), dt_virt_base,
+		       granularity, 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 > granularity)
+		create_mapping(round_down(dt_phys, granularity), dt_virt_base,
+			       round_up(offset + size, granularity), prot);
+
+	memblock_reserve(dt_phys, size);
+
+	return dt_virt;
+}