[U-Boot] [PATCH v2 5/6] sunxi: add code for recalculating the DRAM size in U-Boot

[Icenowy Zheng]

于 2018年4月3日 GMT+08:00 下午7:34:55, Maxime Ripard <maxime.ripard at bootlin.com> 写到:
>On Tue, Apr 03, 2018 at 11:13:17AM +0100, Andre Przywara wrote:
>> >>>> For hacking it, see my implementation in v1, which assumes the
>> >>>> only size supported bigger than 2GiB is 3GiB (which is
>> >>>> acceptable on sunxi, but might not work on other platforms).
>> >>>>
>> >>>> As Andre said, that function has another big problem -- it
>detects
>> >>>> memory with writing to it. This is risky.
>> >>>
>> >>> How is it risky when it's done by the SPL?
>> >>
>> >> Originally that was my confusion as well: It's not the SPL calling
>that
>> >> function. The DRAM controller init function in there knows very
>> >> precisely how much DRAM we have, but we don't communicate this to
>U-Boot
>> >> proper. So U-Boot *proper* goes ahead and probes the DRAM. This
>means it
>> >> could step into secure memory, for instance. On sunxi64 we have
>the ATF
>> >> running between SPL and U-Boot, also all kind of secure payloads
>could
>> >> already have been registered.
>> >> So I wonder if it would be easier to somehow pass on this *one*
>word of
>> >> information between SPL and U-Boot proper to avoid calling this
>function
>> >> altogether?
>> > 
>> > That would definitely make sense yes.
>> 
>> So since the SPL loads the DT anyway (from the FIT image) and puts it
>at
>> the end of the U-Boot (proper) binary, wouldn't it be the easiest to
>> just patch the actual DRAM size in there?
>> IIRC we don't have any FDT write code in the SPL at the moment, and
>> pulling it in would probably push it over the edge again, but:
>
>That assumes that you are loading a FIT image, which might or might
>not be the case, and on most arm32 chips, most likely won't.
>
>I guess we'd need to find another way (put some information in an
>SRAM somewhere?) to try to do that for all variants.

Extend the SPL header again? If we found SPL v3+, use
the DRAM size encoded and bypass ram_get_size,
otherwise fallback to ram_get_size?

(Although it will lead to some days of mess on sunxi-tools,
this is a reasonable choice.)

>
>Maxime