[coreboot] suspend/resume in v3

Kevin O'Connor kevin at koconnor.net
Mon Sep 8 04:34:57 CEST 2008

On Mon, Sep 08, 2008 at 02:28:15AM +0200, Carl-Daniel Hailfinger wrote:
> On 08.09.2008 02:06, Kevin O'Connor wrote:
> > Why can't the code use a new stack after CAR is disabled?
> >
> > To be clear, I think moving the stack would be a bad idea.  However, I
> > don't see why the code can't just start using a new stack.
> >
> > Right now, the only stack variable that is shared between CAR and
> > post-CAR is 'archive' (in stage1_main() ).
> Please update your v3 tree.

Okay - I see it's used more frequently now.

I don't think it fundamentally changes much though.  One could copy
'struct global_vars' to a permanent location before calling stage2.

Doing so would require global_vars() to evaluate to different
locations depending on the stage.  Unfortunately, this would limit
sharing of code between initram and stage2.  Stage2 is compressed
though - is it still a problem?

(An alternative would be to pass the gloval_vars address to every
function that needed it - one could dress it up with macros, but it's
probably too ugly.)

> > This would still require memory under 1MB for car, but at least stage2
> > could run with a full stack and globals that run in reserved memory.
> >
> > Have I missed something?
> Yes. If we can get some memory reserved below 1 MB for CAR, there is no
> need to move the stack. Although the stack does grow quite a bit beyond
> the CAR area once we are post-CAR, we can easily back up all of lowmem
> (or selective chunks of it) in reserved memory at the top of RAM. That
> allows us to leave the stack completely alone until we hand off control
> to the payload (and we won't call a payload for the S3 resume case).

I suspect using ram under 1MB is going to be more problematic than you
think.  I hope to be proven wrong.  :-)

> By the way, here's a nice small problem for you, Kevin: How can we
> combine SeaBIOS and suspend-to-RAM? Either SeaBIOS needs to have its own
> S3 resume path (machine-specific) or we perform VGA init in coreboot.

I thought S3 restore didn't require a BIOS VGA init.  My understanding
was - turn on ram and jump to the OS.  I wasn't sure even if stage2
had to be run.  I'm no expert though.

There is some good info in the acpi spec (do a google search for
'ACPIspec30b.pdf') in section 15.1.3.


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