2.6.28-rc1: NVRAM being corrupted on ppc64 preventing boot (bisected)

[Mel Gorman]

On Thu, Oct 23, 2008 at 09:10:29PM -0700, Linus Torvalds wrote:
> 
> It's been two weeks, so it's time to close the merge window. A 2.6.28-rc1 
> is out there, and it's hopefully all good.
> 

I first encountered this problem in SLES 11 Beta 2 but now I see it
affects 2.6.28-rc1 too.

On some ppc64 machines, NVRAM is being corrupted very early in boot (before
console is initialised). The machine reboots and then fails to find yaboot
printing the error "PReP-BOOT: Unable to load PRep image".  It's nowhere near
as serious as the ftrace+e1000 problem as the machine is not bricked but it's
fairly scary looking, the machine cannot boot and the fix is non-obvious. To
"fix" the machine;

1. Go to OpenFirmware prompt
2. type dev nvram
3. type wipe-nvram

The machine will reboot, reconstruct the NVRAM using some magic and yaboot
work again allowing an older kernel to be used. I bisected the problem down
to this commit.