[PATCH 5/5] arm64/efi: adapt to relaxed FDT placement requirements

[Ard Biesheuvel]

With the relaxed FDT placement requirements in place, we can change
the allocation strategy used by the stub to put the FDT image higher
up in memory. At the same time, reduce the minimal alignment to a
power of 2 upper bound of the size: this way, we are still guaranteed
not to cross a 2 MB boundary, but will potentially waste less memory
doing so.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 arch/arm64/include/asm/efi.h            | 9 ++++-----
 drivers/firmware/efi/libstub/arm-stub.c | 2 +-
 drivers/firmware/efi/libstub/fdt.c      | 7 ++-----
 3 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
index ef572206f1c3..68f7bb2ddad7 100644
--- a/arch/arm64/include/asm/efi.h
+++ b/arch/arm64/include/asm/efi.h
@@ -39,12 +39,11 @@ extern void efi_init(void);
 /* arch specific definitions used by the stub code */
 
 /*
- * AArch64 requires the DTB to be 8-byte aligned in the first 512MiB from
- * start of kernel and may not cross a 2MiB boundary. We set alignment to
- * 2MiB so we know it won't cross a 2MiB boundary.
+ * AArch64 requires the DTB to be 8-byte aligned and not cross a 2MiB boundary.
+ * So align to a power of 2 upper bound of the FDT size.
  */
-#define EFI_FDT_ALIGN	SZ_2M   /* used by allocate_new_fdt_and_exit_boot() */
-#define MAX_FDT_OFFSET	SZ_512M
+#define EFI_FDT_ALIGN(x)	roundup_pow_of_two(x)
+#define MAX_FDT_OFFSET		ULONG_MAX
 
 #define efi_call_early(f, ...) sys_table_arg->boottime->f(__VA_ARGS__)
 
diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index dcae482a9a17..c58c21c22dbe 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -269,7 +269,7 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
 
 	new_fdt_addr = fdt_addr;
 	status = allocate_new_fdt_and_exit_boot(sys_table, handle,
-				&new_fdt_addr, dram_base + MAX_FDT_OFFSET,
+				&new_fdt_addr, MAX_FDT_OFFSET,
 				initrd_addr, initrd_size, cmdline_ptr,
 				fdt_addr, fdt_size);
 
diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
index 91da56c4fd54..1a44d410a63b 100644
--- a/drivers/firmware/efi/libstub/fdt.c
+++ b/drivers/firmware/efi/libstub/fdt.c
@@ -165,10 +165,6 @@ fdt_set_fail:
 	return EFI_LOAD_ERROR;
 }
 
-#ifndef EFI_FDT_ALIGN
-#define EFI_FDT_ALIGN EFI_PAGE_SIZE
-#endif
-
 /*
  * Allocate memory for a new FDT, then add EFI, commandline, and
  * initrd related fields to the FDT.  This routine increases the
@@ -223,7 +219,8 @@ efi_status_t allocate_new_fdt_and_exit_boot(efi_system_table_t *sys_table,
 	 */
 	new_fdt_size = fdt_size + EFI_PAGE_SIZE;
 	while (1) {
-		status = efi_high_alloc(sys_table, new_fdt_size, EFI_FDT_ALIGN,
+		status = efi_high_alloc(sys_table, new_fdt_size,
+					EFI_FDT_ALIGN(new_fdt_size),
 					new_fdt_addr, max_addr);
 		if (status != EFI_SUCCESS) {
 			pr_efi_err(sys_table, "Unable to allocate memory for new device tree.\n");
-- 
1.8.3.2