[U-Boot-Users] [PATCH v2] PPC405EX(r) ECC and SDRAM Initialization Clean-ups

[Grant Erickson]

On 4/28/08 2:27 PM, Wolfgang Denk wrote:
> In message <1209401636-9846-1-git-send-email-gerickson at nuovations.com> you
> wrote:
>> The primary goal of these changes is to unify some of the low-level
>> SDRAM and ECC initialization code for the PPC4xx processors that use a
>> common DDR2 SDRAM controller.
>> 
>> In particular, in the case of the 405EX[r], it must initialize SDRAM
>> before a primordial stack is available since OCM doesn't exist and the
>> data cache does not work for such a purpose. As a consequence, the ECC
>> (and SDRAM) initialization code must be stack-free.
> 
> Stefan already asked this... I would also like to understand why the
> data cache cannot be used for initial RAM as we do on so many other
> systems?

Agreed. The changes were based on the comments in the Kilauea and Makalu
board ports indicating that this had been attempted--twice--and didn't work.

I am escalating with AMCC to find out if this is a processor errata, board
issue or just a programming issue that needs to be investigated further.

> I hesitate to throw away good C code in favour of hard to read,  hard
> to maintain assembly, especially if this also breaks with some of the
> U-Boot design principles.

Again, agreed wholeheartedly though I have to remark that I made a
particular effort to make the assembly as readable and as generalized as
possible.

Regards,

Grant