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sunxi: A64: do an RMR switch if started in AArch32 mode
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> Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com> Reviewed-by: Jagan Teki <jagan@openedev.com>
This commit is contained in:
Andre Przywara
Jagan Teki
parent
b5402d13d4
commit
83843c9b3a
3 changed files with 85 additions and 0 deletions
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@ -4,6 +4,36 @@
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* SPDX-License-Identifier: GPL-2.0+
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*/
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#if defined(CONFIG_RESERVE_ALLWINNER_BOOT0_HEADER) && !defined(CONFIG_SPL_BUILD)
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/* reserve space for BOOT0 header information */
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b reset
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.space 1532
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#elif defined(CONFIG_ARM_BOOT_HOOK_RMR)
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/*
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* Switch into AArch64 if needed.
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* Refer to arch/arm/mach-sunxi/rmr_switch.S for the original source.
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*/
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tst x0, x0 // this is "b #0x84" in ARM
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b reset
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.space 0x7c
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.word 0xe59f1024 // ldr r1, [pc, #36] ; 0x170000a0
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.word 0xe59f0024 // ldr r0, [pc, #36] ; CONFIG_*_TEXT_BASE
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.word 0xe5810000 // str r0, [r1]
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.word 0xf57ff04f // dsb sy
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.word 0xf57ff06f // isb sy
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.word 0xee1c0f50 // mrc 15, 0, r0, cr12, cr0, {2} ; RMR
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.word 0xe3800003 // orr r0, r0, #3
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.word 0xee0c0f50 // mcr 15, 0, r0, cr12, cr0, {2} ; RMR
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.word 0xf57ff06f // isb sy
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.word 0xe320f003 // wfi
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.word 0xeafffffd // b @wfi
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.word 0x017000a0 // writeable RVBAR mapping address
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#ifdef CONFIG_SPL_BUILD
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.word CONFIG_SPL_TEXT_BASE
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#else
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.word CONFIG_SYS_TEXT_BASE
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#endif
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#else
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/* normal execution */
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b reset
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#endif
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41
arch/arm/mach-sunxi/rmr_switch.S
Normal file
41
arch/arm/mach-sunxi/rmr_switch.S
Normal file
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@ -0,0 +1,41 @@
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@
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@ ARMv8 RMR reset sequence on Allwinner SoCs.
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@
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@ All 64-bit capable Allwinner SoCs reset in AArch32 (and continue to
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@ exectute the Boot ROM in this state), so we need to switch to AArch64
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@ at some point.
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@ Section G6.2.133 of the ARMv8 ARM describes the Reset Management Register
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@ (RMR), which triggers a warm-reset of a core and can request to switch
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@ into a different execution state (AArch32 or AArch64).
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@ The address at which execution starts after the reset is held in the
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@ RVBAR system register, which is architecturally read-only.
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@ Allwinner provides a writable alias of this register in MMIO space, so
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@ we can easily set the start address of AArch64 code.
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@ This code below switches to AArch64 and starts execution at the specified
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@ start address. It needs to be assembled by an ARM(32) assembler and
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@ the machine code must be inserted as verbatim .word statements into the
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@ beginning of the AArch64 U-Boot code.
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@ To get the encoded bytes, use:
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@ ${CROSS_COMPILE}gcc -c -o rmr_switch.o rmr_switch.S
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@ ${CROSS_COMPILE}objdump -d rmr_switch.o
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@
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@ The resulting words should be inserted into the U-Boot file at
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@ arch/arm/include/asm/arch-sunxi/boot0.h.
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@
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@ This file is not build by the U-Boot build system, but provided only as a
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@ reference and to be able to regenerate a (probably fixed) version of this
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@ code found in encoded form in boot0.h.
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.text
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ldr r1, =0x017000a0 @ MMIO mapped RVBAR[0] register
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ldr r0, =0x57aA7add @ start address, to be replaced
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str r0, [r1]
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dsb sy
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isb sy
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mrc 15, 0, r0, cr12, cr0, 2 @ read RMR register
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orr r0, r0, #3 @ request reset in AArch64
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mcr 15, 0, r0, cr12, cr0, 2 @ write RMR register
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isb sy
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1: wfi
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b 1b
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@ -142,6 +142,20 @@ config RESERVE_ALLWINNER_BOOT0_HEADER
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blob relies on this information to load and execute U-Boot.
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Only needed on 64-bit Allwinner boards so far when using boot0.
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config ARM_BOOT_HOOK_RMR
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bool
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depends on ARM64
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default y
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select ENABLE_ARM_SOC_BOOT0_HOOK
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---help---
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Insert some ARM32 code at the very beginning of the U-Boot binary
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which uses an RMR register write to bring the core into AArch64 mode.
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The very first instruction acts as a switch, since it's carefully
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chosen to be a NOP in one mode and a branch in the other, so the
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code would only be executed if not already in AArch64.
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This allows both the SPL and the U-Boot proper to be entered in
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either mode and switch to AArch64 if needed.
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config DRAM_TYPE
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int "sunxi dram type"
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depends on MACH_SUN8I_A83T
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