Re: debian-installer: please default to grub-ieee1275 on powerpc instead of yaboot

[Lennart Sorensen]

On Thu, Sep 21, 2017 at 02:49:53PM +0200, Frank Scheiner wrote:
> On 09/21/2017 02:21 PM, John Paul Adrian Glaubitz wrote:
> > [...]
> > What we need are people who are willing to extensively test d-i
> > images with GRUB on powerpc and ppc64 and report back.
> 
> I can offer to test with all sorts of Power Mac G4s and an Xserve G4 for
> powerpc. I still need to buy a few CD-RWs though. :-)
> 
>  Also, I'm
> > not yet sure whether I have understood how exactly GRUB is properly
> > configured and used on powerpc and ppc64.
> 
> (1) Mathieu's pointer to [1] (with Grub's expectations) came a little too
> late for me and the howto I provided on [2].
> 
> (2) It looks like Rogério Brito on [3] wanted to make sure that his Grub
> installation also works with what yaboot "dictated" during installation
> (e.g. 800 KB HFS partition, etc.).
> 
> I'm unsure what the best approach would be. Assuming that on updates to Grub
> a new grub.img needs to be created, with approach (2) only a single file
> needs to be copied to the HFS partition. With approach (1) I actually don't
> know if the HFS partition will contain all the Grub modules in addition. But
> approach (1) seems to be the "default" for Grub and most likely the shipped
> tools also have the same expectations.
> 
> [1]: https://bugs.debian.org/691207
> 
> [2]: https://lists.debian.org/debian-powerpc/2017/09/msg00034.html
> 
> [3]: http://cynic.cc/blog/posts/running_grub2_on_powerpc_macs/

Well in the case of IBM power systems, you use a DOS MBR partition scheme
and you create a Prep boot partition, which should be 1MB or so in size,
and grub is installed there as a raw image.  Has been working fine for
a while as far as I have been able to tell.  The grub modules stay in
whatever /boot is on, and the grub image generated contains enough of
grub to read filesystems and is loaded by the firmware from the prep
boot partition (it litterally reads that partition into ram as raw data,
and executes it).  This is why the prep boot partition has to be large
enough to hold whatever the grub image with required starting modules
needs.

-- 
Len Sorensen