[U-Boot] [U-Boot, 2/3] mpc85xx: Add deep sleep framework support

[Tang Yuantian-B29983 <Yuantian.Tang@freescale.com>]

On 2014/2/25 ??? 3:11, Scott Wood wrote:
>>>> Why what? Why we need it?
>>>>
>>>> It is a help function and used by ASM code in which
>>>> we can't determine whether it is a warm reset boot.
>>> Why don't you just open code it?
>> I can't check the warmboot status in ASM code.
>> In order to get the warmboot status in ASM code, I wrote this function.
> Why can't you check it in asm code?  See lib/asm-offsets.c.
Found it. Still learn how to use it.

Thanks,
Yuantian

>>>>>> +	if (gd->flags & GD_FLG_WARM_BOOT) {
>>>>>> +		src = (u64 *)in_be32(&scfg->sparecr[2]);
>>>>>> +		dst = (u64 *)(0);
>>>>>> +		for (i = 0; i < 128/sizeof(u64); i++) {
>>>>>> +			*dst = *src;
>>>>>> +			dst++;
>>>>>> +			src++;
>>>>>> +		}
>>>>>> +	}
>>>>> (u64 *)(0) is a NULL pointer.  Dereferencing NULL pointers is undefined
>>>>> and GCC has been getting increasingly free with making surprising
>>>>> optimizations based on that (such as assuming any code path that it knows
>>>>> can reach a NULL dereference is dead code and can be removed).
>>>>>
>>>> Then how we operate 0 address if not dereferencing NULL pointer?
>>>>
>>> With an I/O accessor (or other inline asm), a TLB mapping, or using a
>>> different memory location.
>> we found the zero address has benefit.
>> I don't know how to achieve this in inline asm or TLB mapping, could you
>> be more specific or write a example for me?
> Inline asm would be something like:
>
> 	asm("stw %1, 0(%0); stw %2, 4(%0)" : "=r" (dst) :
> 		"r" ((u32)(src >> 32)), "r" ((u32)src));
>
> -Scott
>
>