Bug#594967: Bug #594967: [poulsbo] grub-pc Hangs After "Welcome to GRUB!"

[Colin Watson]

On Mon, Jan 03, 2011 at 12:13:01AM +0000, Colin Watson wrote:
> On Sun, Jan 02, 2011 at 10:41:50PM +0000, Steve McIntyre wrote:
> > 2.iso:
> > 
> >   goes all the way through to bus ff and returns to a grub prompt
> 
> This is interesting and suggests a measure of coincidence.  What that
> patch did was skip remaining functions on a device that doesn't
> implement function 0, taking that as an indication that it doesn't
> exist.  This was based on:
> 
>   http://en.wikipedia.org/wiki/PCI_configuration_space#Bus_enumeration
> 
> Vladimir, are you OK with this change to trunk?
> 
> 2011-01-02  Colin Watson  <cjwatson at ubuntu.com>
> 
> 	* grub-core/bus/pci.c (grub_pci_iterate): Skip remaining functions
> 	on devices that do not implement function 0.

I've applied this patch to trunk following an ack from Vladimir on IRC.
I'll prepare an updated package for unstable shortly.

> Nevertheless, I'm not confident that this will fix the problem on all
> machines, so I would like to sort out the bridge handling as well.

This may be more complicated than I thought.  Seth Goldberg pointed out
that my approach fails to deal with peer host bridges correctly (i.e.
cases where there are multiple trees, not just a single one rooted at
bus 0).  Linux deals with this by asking the PCI BIOS for the last bus
number, but at this point things get complicated as you have to do
things in different ways for different firmware.

I am inclined to try the first piece alone and see how this works out,
and if we can fix the affected systems by just probing function 0 on
every device on every bus then let it stand at that, even if it feels
less elegant.  Inventing new piles of infrastructure to handle a case
I'm unsure about in a subsystem I don't know well isn't my idea of a
good time.

-- 
Colin Watson                                       [cjwatson at debian.org]