arm/arm64: implement a boot header capability

Some SPL loaders (like Allwinner's boot0, and Broadcom's boot0)
require a header before the actual U-Boot binary to both check its
validity and to find other data to load. Sometimes this header may
only be a few bytes of information, and sometimes this might simply
be space that needs to be reserved for a post-processing tool.

Introduce a config option to allow assembler preprocessor commands
to be inserted into the code at the appropriate location; typical
assembler preprocessor commands might be:
  .space 1000
  .word 0x12345678

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Steve Rae <srae@broadcom.com>
Commit Notes:
Please note that the current code:
  start.S (arm64) and
  vectors.S (arm)
already jumps over some portion of data already, so this option basically
just increases the size of this region (and the resulting binary).

For use with Allwinner's boot0 blob there is a tool called boot0img[1],
which fills the header to allow booting A64 based boards.
For the Pine64 we need a 1536 byte header (including the branch
instruction) at the moment, so we add this to the defconfig.

[1] https://github.com/apritzel/pine64/tree/master/tools
END
Reviewed-by: Tom Rini <trini@konsulko.com>

arch/arm/Kconfig

@@ -91,6 +91,14 @@ config SYS_L2CACHE_OFF
 	  If SoC does not support L2CACHE or one do not want to enable
 	  L2CACHE, choose this option.
 
+config ENABLE_ARM_SOC_BOOT0_HOOK
+	bool "prepare BOOT0 header"
+	help
+	  If the SoC's BOOT0 requires a header area filled with (magic)
+	  values, then choose this option, and create a define called
+	  ARM_SOC_BOOT0_HOOK which contains the required assembler
+	  preprocessor code.
+
 choice
 	prompt "Target select"
 	default TARGET_HIKEY

arch/arm/cpu/armv8/start.S

@@ -21,6 +21,16 @@
 _start:
 	b	reset
 
+#ifdef CONFIG_ENABLE_ARM_SOC_BOOT0_HOOK
+/*
+ * Various SoCs need something special and SoC-specific up front in
+ * order to boot, allow them to set that in their boot0.h file and then
+ * use it here.
+ */
+#include <asm/arch/boot0.h>
+ARM_SOC_BOOT0_HOOK
+#endif
+
 	.align 3
 
 .globl	_TEXT_BASE

arch/arm/include/asm/arch-bcm281xx/boot0.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright 2016 Broadcom Corporation.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __BOOT0_H
+#define __BOOT0_H
+
+/* BOOT0 header information */
+#define ARM_SOC_BOOT0_HOOK	\
+	.word	0xbabeface;	\
+	.word	_end - _start
+
+#endif /* __BOOT0_H */

arch/arm/include/asm/arch-sunxi/boot0.h

@@ -0,0 +1,14 @@
+/*
+ * Configuration settings for the Allwinner A64 (sun50i) CPU
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __BOOT0_H
+#define __BOOT0_H
+
+/* reserve space for BOOT0 header information */
+#define ARM_SOC_BOOT0_HOOK	\
+	.space	1532
+
+#endif /* __BOOT0_H */

arch/arm/lib/vectors.S

@@ -60,6 +60,16 @@ _start:
 	ldr	pc, _irq
 	ldr	pc, _fiq
 
+#ifdef CONFIG_ENABLE_ARM_SOC_BOOT0_HOOK
+/*
+ * Various SoCs need something special and SoC-specific up front in
+ * order to boot, allow them to set that in their boot0.h file and then
+ * use it here.
+ */
+#include <asm/arch/boot0.h>
+ARM_SOC_BOOT0_HOOK
+#endif
+
 /*
  *************************************************************************
  *

configs/bcm28155_ap_defconfig

@@ -22,3 +22,4 @@ CONFIG_G_DNL_MANUFACTURER="Broadcom Corporation"
 CONFIG_G_DNL_VENDOR_NUM=0x18d1
 CONFIG_G_DNL_PRODUCT_NUM=0x0d02
 CONFIG_OF_LIBFDT=y
+CONFIG_ENABLE_ARM_SOC_BOOT0_HOOK=y

configs/bcm28155_w1d_defconfig

@@ -22,3 +22,4 @@ CONFIG_USB_GADGET_DOWNLOAD=y
 CONFIG_G_DNL_MANUFACTURER="Broadcom Corporation"
 CONFIG_G_DNL_VENDOR_NUM=0x18d1
 CONFIG_G_DNL_PRODUCT_NUM=0x0d02
+CONFIG_ENABLE_ARM_SOC_BOOT0_HOOK=y

configs/pine64_plus_defconfig

@@ -9,3 +9,4 @@ CONFIG_DEFAULT_DEVICE_TREE="sun50i-a64-pine64-plus"
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_FPGA is not set
+CONFIG_ENABLE_ARM_SOC_BOOT0_HOOK=y