[coreboot] question about post_cache_as_ram() function

[Fengwei Zhang]

> DCACHE_RAM_BASE is the start address of the memory addresses that are used for
> CAR.
>
> DCACHE_RAM_SIZE is the size of that region.
>
I checked the value from Kconfig under /mainboard/asus/m2v-mx_se/
DCACHE_RAM_BASE is 0xcc000
DCACHE_RAM_SIZE is 0x4000
Why does they set to these value? Does them change?
Do they setup by hardware?

> RAMTOP is the highest address of the memory region that coreboot will use in
> RAM.
>
>> In addition, why do we need to set new esp here?
>> 		/* set new esp */ /* before CONFIG_RAMBASE */
>> 		"subl   %0, %%esp\n\t"
>>
>> 		::"a"( (CONFIG_DCACHE_RAM_BASE + CONFIG_DCACHE_RAM_SIZE)-
>> (CONFIG_RAMTOP) )
> This moves the stack from CAR area to RAM.
>
> While in CAR, the stack is laid out at the top end of CAR, growing downwards
> (ie. starting at DCACHE_RAM_BASE + DCACHE_RAM_SIZE).
> While in RAM, it starts at the top end of the ram area used for coreboot
> (RAMTOP).
I see
>
> Before that line the stack is copied from CAR to RAM, then esp is setup so it
> points to the same place in RAM that it pointed to in CAR (that's why we use
> sub, not mov).
i see the copying from CAR to RAM. but I still confused about the value 
of esp. Why is this euqation:
esp = esp - (CONFIG_DCACHE_RAM_BASE + CONFIG_DCACHE_RAM_SIZE)- 
(CONFIG_RAMTOP))

I thought the esp should be: CONFIG_RAMTOP - CONFIG_DCACHE_RAM_SIZE

Thanks!

Best,
Fengwei