[U-Boot] [PATCH v2] arm64: allow space reservation for boot header

[Andre Przywara]

Some SPL loaders (like Allwinner's boot0) require a header before the
actual U-Boot binary to both check its validity and to find other data
to load.
Introduce a config option to reserve some space at the beginning of the
binary to later hold the header if needed.
Please note that the current arm64 start.S jumps over some portion of
data already, so this option bascially just increases this region
to allow post-processing tools to insert more data there.
This also means that both filling the header is optional and also having
some extra space in there does not hurt apart from enlarging the binary.

For the 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.

Signed-off-by: Andre Przywara <andre.przywara at arm.com>

[1] https://github.com/apritzel/pine64/tree/master/tools
---
 arch/arm/cpu/armv8/start.S    | 3 +++
 board/sunxi/Kconfig           | 7 +++++++
 configs/pine64_plus_defconfig | 1 +
 include/configs/sun50i.h      | 4 ++++
 4 files changed, 15 insertions(+)

diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
index e933021..a9cd7e9 100644
--- a/arch/arm/cpu/armv8/start.S
+++ b/arch/arm/cpu/armv8/start.S
@@ -21,6 +21,9 @@
 _start:
 	b	reset
 
+#ifdef CONFIG_START_HEADER_SPACE
+	.space CONFIG_START_HEADER_SPACE /* can be filled with a boot0 header */
+#endif
 	.align 3
 
 .globl	_TEXT_BASE
diff --git a/board/sunxi/Kconfig b/board/sunxi/Kconfig
index fa78720..9f2e17e 100644
--- a/board/sunxi/Kconfig
+++ b/board/sunxi/Kconfig
@@ -15,6 +15,13 @@ config SUNXI_GEN_SUN6I
 	separate ahb reset control registers, custom pmic bus, new style
 	watchdog, etc.
 
+config SUNXI_BOOT0
+	bool "prepare for boot0 header"
+	---help---
+	If U-Boot is loaded from the Allwinner provided boot0 blob, it
+	expects a header area filled with magic values.
+	This option will add some space at the beginning of the image to
+	let a tool later on fill in this header with sensible data.
 
 choice
 	prompt "Sunxi SoC Variant"
diff --git a/configs/pine64_plus_defconfig b/configs/pine64_plus_defconfig
index 0977334..b93e4da 100644
--- a/configs/pine64_plus_defconfig
+++ b/configs/pine64_plus_defconfig
@@ -18,3 +18,4 @@ CONFIG_CMD_EXT2=y
 CONFIG_CMD_EXT4=y
 CONFIG_CMD_FAT=y
 CONFIG_CMD_FS_GENERIC=y
+CONFIG_SUNXI_BOOT0=y
diff --git a/include/configs/sun50i.h b/include/configs/sun50i.h
index 0fdb4c7..6923b60 100644
--- a/include/configs/sun50i.h
+++ b/include/configs/sun50i.h
@@ -17,6 +17,10 @@
 #define GICD_BASE		0x1c81000
 #define GICC_BASE		0x1c82000
 
+#ifdef CONFIG_SUNXI_BOOT0
+#define CONFIG_START_HEADER_SPACE	1532
+#endif
+
 /*
  * Include common sunxi configuration where most the settings are
  */
-- 
2.8.2