[U-Boot] PPC405EX CHIP_21 erratum

[Stefan Roese <sr@denx.de>]

On Monday 02 May 2011 23:44:58 Steven A. Falco wrote:
> I have not been able to find a way to distinguish a power-up versus a
> reboot. So for now, I've implemented the AMCC bug fix more or less as
> written.  To do it right, we'd have to add entries in every U-Boot config
> file for the 405 EX/EXr to definitively specify the CPU type expected, and
> to put the list of allowed PVRs in the code.
> 
> This means that the PVR is essentially useless to distinguish between the
> EX and EXr, because we have seen one misbehaving EX report as an EXr!
> If the PVR had been garbage, we could maybe use it, but reporting "wrong
> yet legal" values makes it worthless.
> 
> All our boards use the EX, so we are able to live with this, but I realize
> it is not a solution for the larger community.  That is why I have not
> proposed a definitive patch.

I see. Thanks for the explanation.

IMHO, it would be best to provide a default list of PVR's that are 
allowed/correct for 405EX(r). And this list can be overridden by a board 
specific version (as needed in your case). Not sure how to handle this 
elegantly in assembler though.

We might move this to cpu_init_f(). This is the first C function called via 
start.S. It already handles similar issues for some 4xx SoC variants 
(reconfigure_pll()) which require a system reboot.

What do you think? Would you be able to prepare a patch with such a CHIP_21 
fix?

Cheers,
Stefan

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