MAIX: CONFIG_SYS_INIT_SP_ADDR

[Sean Anderson]

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