[U-Boot] U-Boot proper(not SPL) relocate option

[Lokesh Vutla]

+ Simon,

On Wednesday 22 November 2017 07:29 AM, Kever Yang wrote:
> Hi Lukasz,
> 
> 
>     Thanks for your quick comments on this topic.
> On 11/21/2017 06:29 PM, Lukasz Majewski wrote:
>> Hi Kever,
>>
>>> Hi Guys,
>>>
>>>       I try to understand why we need to do the relocate in U-Boot.
>>>   From the document README/crt0.S, I think the relocation feature comes
>>> from some SoC have limited SRAM whose size is enough to load the whole
>>> U-Boot, but not enough to run all the drivers.
>>>
>>>       I don't know how many SoCs/Archs still must use this feature,
>>> but I'm sure all
>>> Rockchip SoCs do not need this feature in both SPL and proper U-Boot,
>>> because rockchip using SPL always running in SRAM to init DDR SDRAM,
>>> and after DRAM available always running U-Boot in DRAM.
>> I always thought that u-boot needs relocation to place itself in the
>> "known" area of SDRAM (which ends in its very end).
> 
> I can understand this feature, we always do dram_init_banks() first,
> then we relocate to 'known' area, then will be no risk to access memory.
> I believe there must be some historical reason for some kind of device,
> the relocate feature is a wonderful idea for it.
> 
> In another case, we can also have a choice for not relocate because:
> - we still can have similar 'bdinfo' but without relocate, we can init
> dram info
>     first, and then init SP, malloc area and so on, and then other
> driver init.
> - All solution for Rockchip SoCs at least have 512MByte DRAM,
>     which should be enough for U-Boot and could consider to be 'known'
> area,
>     many other SoCs should be similar.
> - Without relocate we can save many step, some of our customer really
>     care much about the boot time duration.
>     * no need to relocate everything
>     * no need to copy all the code
>     * no need init the driver more than once

I agree that there should be an option for avoiding relocation. There is
a flag "GD_FLG_SKIP_RELOC" which when enabled on gd->flags tries to skip
relocation for u-boot proper.  I am sure that this must be working for
x86 but it can be ported for other architectures as well?

Thanks and regards,
Lokesh