[PATCH 2/8] arm64/kernel: reuse boot_args array to get to __fdt_pointer

[Ard Biesheuvel]

Since we record the boot_args [x0 .. x3] early at boot anyway, there is
no need to keep the FDT address in a callee saved register with file scope
in head.S. So simply refer to boot_args[0] directly in the call to
setup_machine(), and drop the handling of x21 from head.S entirely.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 arch/arm64/kernel/head.S  | 14 ++++++--------
 arch/arm64/kernel/setup.c |  4 +---
 2 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 69b33535911e..9d8f928c355c 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -234,16 +234,15 @@ ENDPROC(stext)
  * Preserve the arguments passed by the bootloader in x0 .. x3
  */
 preserve_boot_args:
-	mov	x21, x0				// x21=FDT
-
-	adr_l	x0, boot_args			// record the contents of
-	stp	x21, x1, [x0]			// x0 .. x3 at kernel entry
-	stp	x2, x3, [x0, #16]
+	adr_l	x4, boot_args			// record the contents of
+	stp	x0, x1, [x4]			// x0 .. x3 at kernel entry
+	stp	x2, x3, [x4, #16]
 
 	dmb	sy				// needed before dc ivac with
 						// MMU off
 
-	add	x1, x0, #0x20			// 4 x 8 bytes
+	mov	x0, x4
+	add	x1, x4, #0x20			// 4 x 8 bytes
 	b	__inval_cache_range		// tail call
 ENDPROC(preserve_boot_args)
 
@@ -480,7 +479,6 @@ __mmap_switched:
 	mov	x4, sp
 	and	x4, x4, #~(THREAD_SIZE - 1)
 	msr	sp_el0, x4			// Save thread_info
-	str_l	x21, __fdt_pointer, x5		// Save FDT pointer
 
 	ldr_l	x4, kimage_vaddr		// Save the offset between
 	sub	x4, x4, x24			// the kernel virtual and
@@ -492,7 +490,7 @@ __mmap_switched:
 #endif
 #ifdef CONFIG_RANDOMIZE_BASE
 	cbnz	x23, 0f				// already running randomized?
-	mov	x0, x21				// pass FDT address in x0
+	ldr_l	x0, boot_args			// pass FDT address in x0
 	bl	kaslr_early_init		// parse FDT for KASLR options
 	cbz	x0, 0f				// KASLR disabled? just proceed
 	mov	x23, x0				// record KASLR offset
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 9dc67769b6a4..83a3e484a90a 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -64,8 +64,6 @@
 #include <asm/xen/hypervisor.h>
 #include <asm/mmu_context.h>
 
-phys_addr_t __fdt_pointer __initdata;
-
 /*
  * Standard memory resources
  */
@@ -304,7 +302,7 @@ void __init setup_arch(char **cmdline_p)
 	early_fixmap_init();
 	early_ioremap_init();
 
-	setup_machine_fdt(__fdt_pointer);
+	setup_machine_fdt(boot_args[0]);
 
 	parse_early_param();
 
-- 
2.5.0