[U-Boot] how to understand "uboot is 32bit program even it is in the 64bit mips"

[Aaron Williams <Aaron.Williams@caviumnetworks.com>]

We have dealt with this in our release of U-Boot since we only support
64-bit Linux. We use the n32 ABI with U-Boot and set it up to use a TLB
entry to map U-Boot into a 32-bit addressable area.

We have some special memcpy type routines that can handle the 64-bit
addressing.

All of our I/O registers require 64-bit addressing so we use assembly
wrappers to do the actual read/writes to those addresses.

-Aaron Williams

On 06/21/2011 07:07 PM, hacklu wrote:
>   I have a 64bit cnMips borad.In the mail list archives,it says  "uboot is 32bit,even in the 64bit cpu."
> but how to understand that?
> I have a guess,is the 64bit cpu support a 32bit-mode,then when does it switch to 64bit-mode to load 64-bit linux?
>
> btw,I have an other question,according to  <see mips run linux>,linux run in the _xkseg_ segment. so the first two bit virtual address in kernel space must be 11,
> like 11xx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx (64bit).
> but when I printf a variable' address in a foo driver,is say 0xa80000041c2ea180. not start of _11_.
> the memory mapping mode has feazed me for _long_ _long_time.
>
> Dear Wolfgang(or someone else who can anwser me),thanks 
>  				
> --------------
> hacklu
> 2011-06-22
>