[coreboot] SeaBIOS debug output

[Jordan Crouse]

On 09/07/08 21:40 -0400, Kevin O'Connor wrote:
> Hi,
> 
> On Wed, Jul 09, 2008 at 11:43:57AM -0600, Myles Watson wrote:
> > On Tue, Jul 8, 2008 at 7:41 PM, Kevin O'Connor <kevin at koconnor.net> wrote:
> > > Did you have coreboot init the vga option rom first?  If so, you
> > > probably want to disable that.
> > 
> > That lets me get farther, which begs the question why it's not
> > reentrant.  Does your code register your handlers over the existing
> > ones?  Should it?
> 
> SeaBIOS has to initialize the 8086 real mode irq vectors on startup.
> It does overwrite the 0x10 handler that the vga bios may have
> installed.  I don't see anyway around this - the contents of the irq
> table could be junk and not initializing it would lead to mysterious
> crashes.

What if coreboot ensured that it wasn't junk before you saw it?

> Also, I don't think we can rely on an emulator to setup the memory
> associated with option roms.  It's fine for initializing the hardware,
> but its another thing to rely on an emulator to initialize the
> software interfaces.
> 
> So, we need to have SeaBIOS do the option rom scan.
> 
> > I'm concerned that in a payload chooser you'll want to have graphical
> > output to allow the user to choose SeaBIOS.  If you can't run the VGA
> > BIOS first ... that seems like a problem.
> 
> This was something that Stefan brought up.  He suggested having
> SeaBIOS return to coreboot and then let coreboot select the payload.
> However, I'm not convinced that this is the best way to go.  Making
> sure that SeaBIOS and coreboot don't stomp on each other could be
> difficult.
> 
> Another possibility is to teach SeaBIOS how to launch payloads from
> flash.
 
We could also make SeaBIOS a special "must absolutely, positively run
first" payload in the chooser so that it executes before we try to
access the display.  I am convinced we can find a reasonable solution
to the problem.

Jordan