[U-Boot] [PATCH 12/24] sunxi: A64: do an RMR switch if started in AArch32 mode

[Andre Przywara]

The Allwinner A64 SoC starts execution in AArch32 mode, and both
the boot ROM and Allwinner's boot0 keep running in this mode.
So U-Boot gets entered in 32-bit, although we want it to run in AArch64.

By using a "magic" instruction, which happens to be an almost-NOP in
AArch64 and a branch in AArch32, we differentiate between being
entered in 64-bit or 32-bit mode.
If in 64-bit mode, we proceed with the branch to reset, but in 32-bit
mode we trigger an RMR write to bring the core into AArch64/EL3 and
re-enter U-Boot at CONFIG_SYS_TEXT_BASE.
This allows a 64-bit U-Boot to be both entered in 32 and 64-bit mode,
so we can use the same start code for the SPL and the U-Boot proper.

Signed-off-by: Andre Przywara <andre.przywara at arm.com>
---
 arch/arm/include/asm/arch-sunxi/boot0.h | 27 +++++++++++++++++++++++++++
 board/sunxi/Kconfig                     |  5 +++++
 2 files changed, 32 insertions(+)

diff --git a/arch/arm/include/asm/arch-sunxi/boot0.h b/arch/arm/include/asm/arch-sunxi/boot0.h
index 6a13db5..c31a2af 100644
--- a/arch/arm/include/asm/arch-sunxi/boot0.h
+++ b/arch/arm/include/asm/arch-sunxi/boot0.h
@@ -4,6 +4,33 @@
  * SPDX-License-Identifier:	GPL-2.0+
  */
 
+#if defined(CONFIG_RESERVE_ALLWINNER_BOOT0_HEADER)
 /* reserve space for BOOT0 header information */
 	b	reset
 	.space	1532
+#elif defined(CONFIG_ARM_BOOT_HOOK_RMR)
+/* switch into AArch64 if needed */
+	tst     x0, x0                  // this is "b #0x84" in ARM
+	b       reset
+	.space  0x7c
+	.word   0xe3a01617              // mov  r1, #0x1700000
+	.word   0xe38110a0              // orr  r1, r1, #0xa0
+	.word   0xe59f0020              // ldr  r0, [pc, #32]
+	.word   0xe5810000              // str  r0, [r1]
+	.word   0xf57ff04f              // dsb  sy
+	.word   0xf57ff06f              // isb  sy
+	.word   0xee1c0f50              // mrc  15, 0, r0, cr12, cr0, {2}
+	.word   0xe3800003              // orr  r0, r0, #3
+	.word   0xee0c0f50              // mcr  15, 0, r0, cr12, cr0, {2}
+	.word   0xf57ff06f              // isb  sy
+	.word   0xe320f003              // wfi
+	.word   0xeafffffd              // b    @wfi
+#ifdef CONFIG_SPL_BUILD
+	.word	CONFIG_SPL_TEXT_BASE
+#else
+	.word   CONFIG_SYS_TEXT_BASE
+#endif
+#else
+/* normal execution */
+	b	reset
+#endif
diff --git a/board/sunxi/Kconfig b/board/sunxi/Kconfig
index 0cd57a2..ba72e76 100644
--- a/board/sunxi/Kconfig
+++ b/board/sunxi/Kconfig
@@ -142,6 +142,11 @@ config RESERVE_ALLWINNER_BOOT0_HEADER
 	blob relies on this information to load and execute U-Boot.
 	Only needed on 64-bit Allwinner boards so far when using boot0.
 
+config ARM_BOOT_HOOK_RMR
+	bool
+	default y if ARM64
+	select ENABLE_ARM_SOC_BOOT0_HOOK
+
 config DRAM_TYPE
 	int "sunxi dram type"
 	depends on MACH_SUN8I_A83T
-- 
2.8.2