On 19/11/2020 19:59, Priit Laes wrote:
> On Thu, Nov 19, 2020 at 10:54:42AM +0000, Andre Przywara wrote:
>> So far we did not support the BootROM based FEL USB debug mode on the
>> 64-bit builds for Allwinner SoCs: The BootROM is using AArch32, but the
>> SPL runs in AArch64.
>> Returning back to AArch32 was not working as expected, since the RMR
>> reset into 32-bit mode always starts execution in the BootROM, but not
>> in the FEL routine.
>>
>> After some debug and research and with help via IRC, the CPU hotplug
>> mechanism emerged as a solution: If a certain R_CPUCFG register contains
>> some magic, the BootROM will immediately branch to an address stored in
>> some other register. This works well for our purposes.
>>
>> Enable the FEL feature by providing early AArch32 code to first save the
>> FEL state, *before* initially entering AArch64.
>> If we eventually determine that we should return to FEL, we reset back
>> into AArch32, and use the CPU hotplug mechanism to run some small
>> AArch32 code snippet that restores the initially saved FEL state.
>>
>> That allows the normal AArch64 SPL build to be loaded via the sunxi-fel
>> tool, with it returning into FEL mode, so that other payloads can be
>> transferred via FEL as well.
>>
>> Tested on A64, H5 and H6.
>>
>> Signed-off-by: Andre Przywara <andre.przyw...@arm.com>
>> ---
>> arch/arm/cpu/armv8/Makefile | 2 +
>> arch/arm/cpu/armv8/fel_utils.S | 78 +++++++++++++++++++++++++
>> arch/arm/include/asm/arch-sunxi/boot0.h | 14 +++++
>> include/configs/sunxi-common.h | 2 -
>> 4 files changed, 94 insertions(+), 2 deletions(-)
>> create mode 100644 arch/arm/cpu/armv8/fel_utils.S
>
> Don't you want to also update board/sunxi/README.sunxi64 ?
Yes, but I am in the process of rewriting this anyway, since some parts
apply to 32-bit SoCs as well (SD card, SPI flash), and there is
currently no documentation about them. So bear with me, I will post a
documentation update ASAP, just didn't want to hold back this patch.
Thanks!
Andre.
>>
>> diff --git a/arch/arm/cpu/armv8/Makefile b/arch/arm/cpu/armv8/Makefile
>> index 93d26f98568..f7b4a5ee46c 100644
>> --- a/arch/arm/cpu/armv8/Makefile
>> +++ b/arch/arm/cpu/armv8/Makefile
>> @@ -27,6 +27,8 @@ obj-$(CONFIG_ARM_SMCCC) += smccc-call.o
>>
>> ifndef CONFIG_SPL_BUILD
>> obj-$(CONFIG_ARMV8_SPIN_TABLE) += spin_table.o spin_table_v8.o
>> +else
>> +obj-$(CONFIG_ARCH_SUNXI) += fel_utils.o
>> endif
>> obj-$(CONFIG_$(SPL_)ARMV8_SEC_FIRMWARE_SUPPORT) += sec_firmware.o
>> sec_firmware_asm.o
>>
>> diff --git a/arch/arm/cpu/armv8/fel_utils.S b/arch/arm/cpu/armv8/fel_utils.S
>> new file mode 100644
>> index 00000000000..334fdef7fa0
>> --- /dev/null
>> +++ b/arch/arm/cpu/armv8/fel_utils.S
>> @@ -0,0 +1,78 @@
>> +/*
>> + * Utility functions for FEL mode, when running SPL in AArch64.
>> + *
>> + * Copyright (c) 2017 Arm Ltd.
>> + *
>> + * SPDX-License-Identifier: GPL-2.0+
>> + */
>> +
>> +#include <asm-offsets.h>
>> +#include <config.h>
>> +#include <asm/system.h>
>> +#include <linux/linkage.h>
>> +
>> +/*
>> + * We don't overwrite save_boot_params() here, to save the FEL state upon
>> + * entry, since this would run *after* the RMR reset, which clobbers that
>> + * state.
>> + * Instead we store the state _very_ early in the boot0 hook, *before*
>> + * resetting to AArch64.
>> + */
>> +
>> +/*
>> + * The FEL routines in BROM run in AArch32.
>> + * Reset back into 32-bit mode here and restore the saved FEL state
>> + * afterwards.
>> + * Resetting back into AArch32/EL3 using the RMR always enters the BROM,
>> + * but we can use the CPU hotplug mechanism to branch back to our code
>> + * immediately.
>> + */
>> +ENTRY(return_to_fel)
>> + /*
>> + * the RMR reset will clear all registers, so save the arguments
>> + * (LR and SP) in the fel_stash structure, which we read anyways later
>> + */
>> + adr x2, fel_stash
>> + str w0, [x2]
>> + str w1, [x2, #4]
>> +
>> + adr x1, fel_stash_addr // to find the fel_stash address in AA32
>> + str w2, [x1]
>> +
>> + ldr x0, =0xfa50392f // CPU hotplug magic
>> +#ifndef CONFIG_MACH_SUN50I_H6
>> + ldr x2, =(SUNXI_CPUCFG_BASE + 0x1a4) // offset for CPU hotplug base
>> + str w0, [x2, #0x8]
>> +#else
>> + ldr x2, =(SUNXI_RTC_BASE + 0x1b8) // BOOT_CPU_HP_FLAG_REG
>> + str w0, [x2], #0x4
>> +#endif
>> + adr x0, back_in_32
>> + str w0, [x2]
>> +
>> + dsb sy
>> + isb sy
>> + mov x0, #2 // RMR reset into AArch32
>> + dsb sy
>> + msr RMR_EL3, x0
>> + isb sy
>> +1: wfi
>> + b 1b
>> +
>> +/* AArch32 code to restore the state from fel_stash and return back to FEL.
>> */
>> +back_in_32:
>> + .word 0xe59f0028 // ldr r0, [pc, #40] ; load fel_stash address
>> + .word 0xe5901008 // ldr r1, [r0, #8]
>> + .word 0xe129f001 // msr CPSR_fc, r1
>> + .word 0xf57ff06f // isb
>> + .word 0xe590d000 // ldr sp, [r0]
>> + .word 0xe590e004 // ldr lr, [r0, #4]
>> + .word 0xe5901010 // ldr r1, [r0, #16]
>> + .word 0xee0c1f10 // mcr 15, 0, r1, cr12, cr0, {0} ; VBAR
>> + .word 0xe590100c // ldr r1, [r0, #12]
>> + .word 0xee011f10 // mcr 15, 0, r1, cr1, cr0, {0} ; SCTLR
>> + .word 0xf57ff06f // isb
>> + .word 0xe12fff1e // bx lr ; return to FEL
>> +fel_stash_addr:
>> + .word 0x00000000 // receives fel_stash addr, by AA64 code above
>> +ENDPROC(return_to_fel)
>> diff --git a/arch/arm/include/asm/arch-sunxi/boot0.h
>> b/arch/arm/include/asm/arch-sunxi/boot0.h
>> index 54c144afd8c..46d0f0666c2 100644
>> --- a/arch/arm/include/asm/arch-sunxi/boot0.h
>> +++ b/arch/arm/include/asm/arch-sunxi/boot0.h
>> @@ -15,6 +15,19 @@
>> tst x0, x0 // this is "b #0x84" in ARM
>> b reset
>> .space 0x7c
>> +
>> + .word 0xe28f0058 // add r0, pc, #88
>> + .word 0xe59f1054 // ldr r1, [pc, #84]
>> + .word 0xe0800001 // add r0, r0, r1
>> + .word 0xe580d000 // str sp, [r0]
>> + .word 0xe580e004 // str lr, [r0, #4]
>> + .word 0xe10fe000 // mrs lr, CPSR
>> + .word 0xe580e008 // str lr, [r0, #8]
>> + .word 0xee11ef10 // mrc 15, 0, lr, cr1, cr0, {0}
>> + .word 0xe580e00c // str lr, [r0, #12]
>> + .word 0xee1cef10 // mrc 15, 0, lr, cr12, cr0, {0}
>> + .word 0xe580e010 // str lr, [r0, #16]
>> +
>> .word 0xe59f1024 // ldr r1, [pc, #36] ; 0x170000a0
>> .word 0xe59f0024 // ldr r0, [pc, #36] ; CONFIG_*_TEXT_BASE
>> .word 0xe5810000 // str r0, [r1]
>> @@ -36,6 +49,7 @@
>> #else
>> .word CONFIG_SYS_TEXT_BASE
>> #endif
>> + .word fel_stash - .
>> #else
>> /* normal execution */
>> b reset
>> diff --git a/include/configs/sunxi-common.h b/include/configs/sunxi-common.h
>> index a6a4879523a..203cb10fbab 100644
>> --- a/include/configs/sunxi-common.h
>> +++ b/include/configs/sunxi-common.h
>> @@ -163,9 +163,7 @@
>>
>> #define CONFIG_SYS_MONITOR_LEN (768 << 10) /* 768 KiB */
>>
>> -#ifndef CONFIG_ARM64 /* AArch64 FEL support is not ready yet
>> */
>> #define CONFIG_SPL_BOARD_LOAD_IMAGE
>> -#endif
>>
>> /*
>> * We cannot use expressions here, because expressions won't be evaluated in
>> --
>> 2.17.5
>>
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