MAIX: CONFIG_SYS_INIT_SP_ADDR

[Heinrich Schuchardt]

Am 9. August 2020 18:35:45 MESZ schrieb Sean Anderson <seanga2 at gmail.com>:
>On 8/9/20 12:14 PM, Heinrich Schuchardt wrote:
>> Hello Sean,
>> 
>> while trying to understand the handling of SMP I stumbled of this
>question:
>> 
>> Why did you define CONFIG_SYS_INIT_SP_ADDR as an odd number on the
>MAIX
>> in commit a7c81fc85326 ("riscv: Add Sipeed Maix support") while the
>> other RISC-V boards use an even number:
>> 
>> include/configs/sifive-fu540.h:29:
>>    29 | #define CONFIG_SYS_INIT_SP_ADDR  (CONFIG_SYS_SDRAM_BASE +
>SZ_2M)
>> 
>> include/configs/qemu-riscv.h:22:
>>    22 | #define CONFIG_SYS_INIT_SP_ADDR  (CONFIG_SYS_SDRAM_BASE +
>SZ_2M)
>> 
>> include/configs/sipeed-maix.h:13:
>>    13 | #define CONFIG_SYS_INIT_SP_ADDR 0x803FFFFF
>> 
>> I always thought that RISC-V stack pointers must be 16 byte aligned:
>> 
>> Cf. https://riscv.org/wp-content/uploads/2015/01/riscv-calling.pdf
>> 
>> "In the standard RISC-V calling convention, the stack grows downward
>and
>> the stack pointer is always kept 16-byte aligned."
>
>Because that is the top of (non-ai) ram. And it gets 16-byte aligned by
>call_board_init_f anyway.
>
>--Sean

Top of RAM is the place to which we want to relocate U-Boot. But furthermore this value minus a multiple of16KiB is also used for the stack lication of the secondary CPU.

Shouldn't we better use the same definition as the other boards?