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.
Also add arch/arm/mach-sunxi/rmr_switch.S, which contains the original ARM assembly code and instructions how to re-generate the encoded version.
Signed-off-by: Andre Przywara andre.przywara@arm.com --- arch/arm/include/asm/arch-sunxi/boot0.h | 30 ++++++++++++++++++++++++ arch/arm/mach-sunxi/rmr_switch.S | 41 +++++++++++++++++++++++++++++++++ board/sunxi/Kconfig | 14 +++++++++++ 3 files changed, 85 insertions(+) create mode 100644 arch/arm/mach-sunxi/rmr_switch.S
diff --git a/arch/arm/include/asm/arch-sunxi/boot0.h b/arch/arm/include/asm/arch-sunxi/boot0.h index 6a13db5..9c6d82d 100644 --- a/arch/arm/include/asm/arch-sunxi/boot0.h +++ b/arch/arm/include/asm/arch-sunxi/boot0.h @@ -4,6 +4,36 @@ * 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. + * Refer to arch/arm/mach-sunxi/rmr_switch.S for the original source. + */ + 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/arch/arm/mach-sunxi/rmr_switch.S b/arch/arm/mach-sunxi/rmr_switch.S new file mode 100644 index 0000000..cefa930 --- /dev/null +++ b/arch/arm/mach-sunxi/rmr_switch.S @@ -0,0 +1,41 @@ +@ +@ ARMv8 RMR reset sequence on Allwinner SoCs. +@ +@ All 64-bit capable Allwinner SoCs reset in AArch32 (and continue to +@ exectute the Boot ROM in this state), so we need to switch to AArch64 +@ at some point. +@ Section G6.2.133 of the ARMv8 ARM describes the Reset Management Register +@ (RMR), which triggers a warm-reset of a core and can request to switch +@ into a different execution state (AArch32 or AArch64). +@ The address at which execution starts after the reset is held in the +@ RVBAR system register, which is architecturally read-only. +@ Allwinner provides a writable alias of this register in MMIO space, so +@ we can easily set the start address of AArch64 code. +@ This code below switches to AArch64 and starts execution at the specified +@ start address. It needs to be assembled by an ARM(32) assembler and +@ the machine code must be inserted as verbatim .word statements into the +@ beginning of the AArch64 U-Boot code. +@ To get the encoded bytes, use: +@ ${CROSS_COMPILE}gcc -c -o rmr_switch.o rmr_switch.S +@ ${CROSS_COMPILE}objdump -d rmr_switch.o +@ +@ The resulting words should be inserted into the U-Boot file at +@ arch/arm/include/asm/arch-sunxi/boot0.h. +@ +@ This file is not build by the U-Boot build system, but provided only as a +@ reference and to be able to regenerate a (probably fixed) version of this +@ code found in encoded form in boot0.h. + +.text + + ldr r1, =0x017000a0 @ MMIO mapped RVBAR[0] register + ldr r0, =0x57aA7add @ start address, to be replaced + str r0, [r1] + dsb sy + isb sy + mrc 15, 0, r0, cr12, cr0, 2 @ read RMR register + orr r0, r0, #3 @ request reset in AArch64 + mcr 15, 0, r0, cr12, cr0, 2 @ write RMR register + isb sy +1: wfi + b 1b diff --git a/board/sunxi/Kconfig b/board/sunxi/Kconfig index 0cd57a2..f020573 100644 --- a/board/sunxi/Kconfig +++ b/board/sunxi/Kconfig @@ -142,6 +142,20 @@ 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 + depends on ARM64 + default y + select ENABLE_ARM_SOC_BOOT0_HOOK + ---help--- + Insert some ARM32 code at the very beginning of the U-Boot binary + which uses an RMR register write to bring the core into AArch64 mode. + The very first instruction acts as a switch, since it's carefully + chosen to be a NOP in one mode and a branch in the other, so the + code would only be executed if not already in AArch64. + This allows both the SPL and the U-Boot proper to be entered in + either mode and switch to AArch64 if needed. + config DRAM_TYPE int "sunxi dram type" depends on MACH_SUN8I_A83T