[U-Boot] 36-bits U-Boot

[Timur Tabi]

On Fri, Oct 22, 2010 at 5:57 AM, Leif Sörman <leif.sorman at enea.com> wrote:
> I want to have ram memory above 4G on a freescale p4080 board since I want to test that 36-bits physical addressing is working, my board has two 2G dimm mounted.

We've tested up to 8GB on a P4080DS.

> The standard 32-bits u-boot on the board says that it can only handle memory less than 4G.
>
> I have managed to flashed a 36-bits u-boot to the board and now I realized that the 36-bits u-boot
>
> put the two gigs memory below 4G.

The purpose of a 36-bit U-Boot is so that you can have more than 2GB
of RAM.  I/O devices are placed above 4GB.

> Is it possible to change something in u-boot so it put one of the memory device above 4G?

Not really.  U-Boot's internal design has quite a few dependencies on
having memory starting at address 0.  Also, getting the Linux kernel
to boot at an address other than 0 is difficult.

Also, even if you have 8GB of memory, it's hard to get Linux to
allocate memory above the 4GB range.

> I think a better solution for me would be to replace the two memory devices with two 4 gigs devices.

Yes, I agree.

> Does u-boot support larger devices?

Yes.  The latest upstream U-Boot supports 4GB DDR and maybe even 8GB DDR.

> Maybe it's only to put the larger memory in and everything works.

It should.

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-- 
Timur Tabi
Linux kernel developer at Freescale