arm64: add an option to switch visibility of CONFIG_SYS_INIT_SP_BSS_OFFSET

By default, CONFIG_SYS_INIT_SP_BSS_OFFSET was made invisible by not
giving a prompt to it.

The only way to define it is to hard-code an extra entry in SoC/board
Kconfig, like arch/arm/mach-tegra/tegra{186,210}/Kconfig.

Add a prompt to it in order to allow defconfig files to specify the
value of CONFIG_SYS_INIT_SP_BSS_OFFSET.

With this, CONFIG_SYS_INIT_SP_BSS_OFFSET would become always visible.
So, we need a new bool option to turn it off by default.

I move the 'default 524288' to the common place. This value is not too
big, but is big enough to avoid the overwrap of DT in most platforms.
If 512KB is not a suitable choice for your platform, you can change it
from your defconfig or menuconfig etc.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Stephen Warren <swarren@nvidia.com>

Makefile

@@ -874,7 +874,7 @@ ifneq ($(CONFIG_BUILD_TARGET),)
 ALL-y += $(CONFIG_BUILD_TARGET:"%"=%)
 endif
 
-ifneq ($(CONFIG_SYS_INIT_SP_BSS_OFFSET),)
+ifdef CONFIG_INIT_SP_RELATIVE
 ALL-y += init_sp_bss_offset_check
 endif
 
@@ -1155,7 +1155,7 @@ binary_size_check: u-boot-nodtb.bin FORCE
 		fi \
 	fi
 
-ifneq ($(CONFIG_SYS_INIT_SP_BSS_OFFSET),)
+ifdef CONFIG_INIT_SP_RELATIVE
 ifneq ($(CONFIG_SYS_MALLOC_F_LEN),)
 subtract_sys_malloc_f_len = space=$$(($${space} - $(CONFIG_SYS_MALLOC_F_LEN)))
 else

arch/arm/Kconfig

@@ -20,15 +20,25 @@ config POSITION_INDEPENDENT
 	  information that is embedded into the binary to support U-Boot
 	  relocating itself to the top-of-RAM later during execution.
 
-config SYS_INIT_SP_BSS_OFFSET
-	int
+config INIT_SP_RELATIVE
+	bool "Specify the early stack pointer relative to the .bss section"
 	help
 	  U-Boot typically uses a hard-coded value for the stack pointer
-	  before relocation. Define this option to instead calculate the
+	  before relocation. Enable this option to instead calculate the
 	  initial SP at run-time. This is useful to avoid hard-coding addresses
 	  into U-Boot, so that can be loaded and executed at arbitrary
-	  addresses and thus avoid using arbitrary addresses at runtime. This
-	  option's value is the offset added to &_bss_start in order to
+	  addresses and thus avoid using arbitrary addresses at runtime.
+
+	  If this option is enabled, the early stack pointer is set to
+	  &_bss_start with a offset value added. The offset is specified by
+	  SYS_INIT_SP_BSS_OFFSET.
+
+config SYS_INIT_SP_BSS_OFFSET
+	int "Early stack offset from the .bss base address"
+	depends on INIT_SP_RELATIVE
+	default 524288
+	help
+	  This option's value is the offset added to &_bss_start in order to
 	  calculate the stack pointer. This offset should be large enough so
 	  that the early malloc region, global data (gd), and early stack usage
 	  do not overlap any appended DTB.

arch/arm/cpu/armv8/linux-kernel-image-header-vars.h

@@ -48,7 +48,7 @@
 #define __MAX(a, b)		(((a) > (b)) ? (a) : (b))
 #define __CODE_DATA_SIZE	(__bss_start - _start)
 #define __BSS_SIZE		(__bss_end - __bss_start)
-#ifdef CONFIG_SYS_INIT_SP_BSS_OFFSET
+#ifdef CONFIG_INIT_SP_RELATIVE
 #define __MAX_EXTRA_RAM_USAGE	__MAX(__BSS_SIZE, CONFIG_SYS_INIT_SP_BSS_OFFSET)
 #else
 #define __MAX_EXTRA_RAM_USAGE	__BSS_SIZE

arch/arm/lib/crt0_64.S

@@ -72,7 +72,7 @@ ENTRY(_main)
 	ldr	x0, =(CONFIG_TPL_STACK)
 #elif defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
 	ldr	x0, =(CONFIG_SPL_STACK)
-#elif defined(CONFIG_SYS_INIT_SP_BSS_OFFSET)
+#elif defined(CONFIG_INIT_SP_RELATIVE)
 	adr	x0, __bss_start
 	add	x0, x0, #CONFIG_SYS_INIT_SP_BSS_OFFSET
 #else

arch/arm/mach-tegra/Kconfig

@@ -86,6 +86,7 @@ config TEGRA_ARMV7_COMMON
 config TEGRA_ARMV8_COMMON
 	bool "Tegra 64-bit common options"
 	select ARM64
+	select INIT_SP_RELATIVE
 	select LINUX_KERNEL_IMAGE_HEADER
 	select POSITION_INDEPENDENT
 	select TEGRA_COMMON

arch/arm/mach-tegra/tegra186/Kconfig

@@ -21,9 +21,6 @@ endchoice
 config SYS_SOC
 	default "tegra186"
 
-config SYS_INIT_SP_BSS_OFFSET
-	default 524288
-
 source "board/nvidia/p2771-0000/Kconfig"
 
 endif

arch/arm/mach-tegra/tegra210/Kconfig

@@ -40,9 +40,6 @@ endchoice
 config SYS_SOC
 	default "tegra210"
 
-config SYS_INIT_SP_BSS_OFFSET
-	default 524288
-
 source "board/nvidia/e2220-1170/Kconfig"
 source "board/nvidia/p2371-0000/Kconfig"
 source "board/nvidia/p2371-2180/Kconfig"