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

[Andre Przywara <andre.przywara@arm.com>]

Hi,

On 21/11/16 16:34, Alexander Graf wrote:
> 
> 
> On 20/11/2016 15:57, Andre Przywara wrote:
>> 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@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
> 
> Is this address guaranteed to stay the same for newer chips?

AW and stay the same? ;-)

> Maybe it'd
> be better to use a pc-relative load and put it in as .word like you do
> below for the text base address.

Yes, good plan.

Cheers,
Andre

> 
> 
> Alex
> 
>> +    .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
>>