[U-Boot] [PATCH v2 11/23] 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.

We use the existing custom header (boot0.h) functionality, but restrict
the existing boot0 header reservation to the non-SPL build now. A SPL
wouldn't need such header anyway. This allows to have both options
defined and lets us use one for the SPL and the other for 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..7799a03 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) && !defined(CONFIG_SPL_BUILD)
 /* 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	0xe59f1024	// ldr     r1, [pc, #36] ; 0x170000a0
+	.word	0xe59f0024	// ldr     r0, [pc, #36] ; CONFIG_*_TEXT_BASE
+	.word	0xe5810000	// str     r0, [r1]
+	.word	0xf57ff04f	// dsb     sy
+	.word	0xf57ff06f	// isb     sy
+	.word	0xee1c0f50	// mrc     15, 0, r0, cr12, cr0, {2} ; RMR
+	.word	0xe3800003	// orr     r0, r0, #3
+	.word	0xee0c0f50	// mcr     15, 0, r0, cr12, cr0, {2} ; RMR
+	.word	0xf57ff06f	// isb     sy
+	.word	0xe320f003	// wfi
+	.word	0xeafffffd	// b       @wfi
+	.word	0x017000a0	// writeable RVBAR mapping address
+#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