Re: [PATCH] move grub_stop() (Re: [PATCH] i386-qemu port)

[Pavel Roskin <proski@gnu.org>]

On Sun, 2009-06-21 at 21:25 +0200, Robert Millan wrote:
> On Sun, Jun 21, 2009 at 03:05:56PM -0400, Pavel Roskin wrote:
> > On Sun, 2009-06-21 at 20:54 +0200, Robert Millan wrote:
> > > Move grub_stop to init.c to ease code sharing with i386-qemu.
> > 
> > That's not quite a movement.  grub_cpu_idle() does nothing.
> 
> Well, the major problem with grub_cpu_idle() doing nothing on coreboot
> is CPU consumption during polls.  grub_stop() is quite a corner case,
> only seen when you hit an error.

I think this should do the right thing if our goal is to stop:

	cli
halt:
	hlt
	jmp halt

The last "jmp" is just in case for non-maskable interrupts.

> > I think we need to have several implementations of grub_stop: hard halt
> > with interrupts disabled, exit from qemu, exit from other emulators if
> > it's different, power off, exit to BIOS.  Then different platforms
> > should enable and try whatever is appropriate for them.
> 
> Note that we already have:
> 
>   grub_stop: Just hang.
> 
>   grub_exit: Exit to BIOS/whatever.  On coreboot (and on i386-qemu)
>   there's really no "proper" thing to do.  Maybe fallback to
>   grub_halt or grub_fatal.
> 
>   grub_halt: Power off.  Theoretically we can have it anywhere,
>   although in some platforms like coreboot it's not easy; otherwise
>   it can fallback to grub_stop.
> 
> I think grub_stop is intended to have this behaviour in all platforms.
> But I'm not sure how useful is it.  Perhaps it could be ditched in
> favour of grub_exit?

From the user's standpoint, I think three "stop-like" calls make sense:

Try to exit so that BIOS can try another media.  Failing that, hang.
That would be appropriate for installations on disks that may or may not
be bootable.  That's grub_exit().

Try for power down the system (that includes telling the emulator to
stop).  Failing that, hang.  That would be appropriate for data centers
where we don't want non-functioning systems to consume power.  That's
grub_halt().

Just stop.  Appropriate if there is an important message on the screen
that the user must see.

-- 
Regards,
Pavel Roskin