[U-Boot] T4QDS e6500 core and U-Boot 64-bit

[Scott Wood]

On Thu, 2014-01-23 at 11:13 -0700, Danny Gale wrote:
> Hi Wolfgang,
> 
> Thanks for your reply. My responses are inline below.
> 
> On 1/22/2014 2:06 AM, Wolfgang Denk wrote:
> > Dear Danny Gale,
> >
> > In message <52DF18B3.1080904 at coloradoengineeringinc.com> you wrote:
> >> The T4240 on the T4QDS board is a PPC e6500 core (64 bit), but it is
> >> configured in U-Boot as an e500 core, which is 32 bit. Why is this?
> > Becuase it simply works :-)
> >
> >> Can it be updated to e6500?
> > Yes - if you add support for 64 bit configurations in general, and
> > for powerpc64 in particular.
> I don't even have a sense for what would be involved here. How 
> fundamentally would the U-Boot code need to change?

The common U-Boot code should be more or less OK -- the armv8 target
runs as 64-bit, and sandbox can as well.  The PPC code is another
matter, though.  You'd need to hack up or replace a bunch of asm code at
the least.

> >> This leads directly into another question: can U-Boot be compiled and
> >> run 64-bit? So far, I have been unable to make it work with a 64-bit
> >> compiler. I'm running into these errors:
> > Not out of the box.
> >
> >
> > What is your actual reason for wanting to run a 64 bit boot loader?
> My reason for wanting to run 64-bit is that this system has 12 GB of 
> RAM. Will 32-bit U-Boot be able to access and test more than 4 GB of RAM?

32-bit U-Boot can detect (or otherwise know about) and tell the OS about
large amounts of RAM, but it can only directly access 2 GiB.

-Scott