[U-Boot] RFC: Aligning arch initialisation sequences

[Reinhard Meyer]

Dear Graeme Russ,
> On 15/11/10 00:46, Reinhard Meyer wrote:
>> Dear Wolfgang Denk,
>>
>> To make it crystal clear now, and put the complete context:
>>
>> That simple change would rid us of all alignment concerns:
>> Setting stack to end of initial storage will certainly
>> be aligned, and the auto_gd will be aligned as the
>> toolchain deems necessary.
>>
>> We would not need GENERATED_GBL_DATA_SIZE anymore.
>>
>> The auto_gd space on stack will be valid even into the call
>> to relocate_code.
>>
>>> void board_init_f (ulong bootflag)
>>> {
>>> 	bd_t *bd;
>>> 	init_fnc_t **init_fnc_ptr;
>>> 	gd_t *id;
>>> 	ulong addr, addr_sp;
>>> +	gd_t auto_gd;
>>>
>>> 	/* Pointer is writable since we allocated a register for it */
>>> -	gd = (gd_t *) (CONFIG_SYS_INIT_SP_ADDR);
>>> +	gd =&auto_gd;
>>> 	/* compiler optimization barrier needed for GCC>= 3.4 */
>>> /* Q: why is that needed anyway ??? */
>>> 	__asm__ __volatile__("": : :"memory");
>>>
>>> 	memset ((void*)gd, 0, sizeof (gd_t));
>>> ....
>>> 	debug ("relocation Offset is: %08lx\n", gd->reloc_off);
>>> 	memcpy (id, (void *)gd, sizeof (gd_t));
>>>
>>> 	relocate_code (addr_sp, id, addr);
>>>
>>> 	/* NOTREACHED - relocate_code() does not return */
>>> }
>>>
>>> This, and setting CONFIG_SYS_INIT_SP_ADDR to an aligned value in
>>> initial storage (SRAM, pinned down Cache, or other) removes alot
>>> of the headache about making stuff aligned.
>>>
>>
>> This three line change DOES NOT propose any different method
>> of handling gd other then it is currently done.
>>
>> It is ONLY a more elegant way to allocate the pre-relocation
>> storage for gd.
>
> On the proviso that gd is not needed _BEFORE_ board_init_f()

At least on ARM, board_init_f() is the first C function called
after basic SoC initialisation in ASM.

And may patch does not move the point of availability of gd at all.

Best Regards,
Reinhard