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

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Date:	Fri, 31 Oct 2008 11:31:16 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	benh@...nel.crashing.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...abs.org
Subject: Re: 2.6.28-rc1: NVRAM being corrupted on ppc64 preventing boot (bisected)

On Fri, Oct 31, 2008 at 10:10:55PM +1100, Paul Mackerras wrote:
> Mel Gorman writes:
> 
> > Yaboot in my case and I've heard it affected a DVD installation. I don't
> > know for sure if it affects netboot but as I think it's something the
> > kernel is doing, it probably doesn't matter how it gets loaded?
> 
> What changed in that commit was the contents of a couple of structures
> that the firmware looks at to see what the kernel wants from
> firmware.  Specifically the change was to say that the kernel (or
> really the zImage wrapper) would like the firmware to be based at the
> 32MB point (which is what AIX uses) rather than 12MB (which was the
> default on older machines).
> 
> So, as I understand it, it's not anything the kernel is actively
> doing, it's how the firmware is reacting to what the kernel says it
> wants.  And since we are requesting the same value as AIX (as far as I
> know) I'm really surprised it caused problems.
> 

Same here, it sounds like an innocent change. While it is possible that AIX
could not work on this machine, it seems a bit unlikely.

> We can revert that commit, but I still need to solve the problem that
> the distros are facing, namely that their installer kernel + initramfs
> images are now bigger than 12MB and can't be loaded if the firmware is
> based at 12MB.  That's why I really want to understand the problem in
> more detail.
> 
> > It's been pointed out that it can be "fixed" by upgrading the firmware but
> > surely we can avoid breaking the machine in the first place?
> 
> Have you upgraded the firmware on the machine you saw this problem on?

No. Luckily for us, it was scheduled to be upgraded but it got delayed
:). I've asked the guy to go somewhere else for a while so I should be able
to keep the machine in the state it's currently in.

> If not, would you be willing to run some tests for me?
> 

Of course. 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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