[Libreboot] GRUB can hang for ~ 3mins due to problematic DVD/CDROM drives on T400 (& possibly other models); workaround explained herein

[Bradley M. Kuhn]

As has been discussed earlier on this thread, problematic DVD and CDROM
drives can cause libreboot's GRUB to hang for up to three minutes.

You can test whether you have this problem by hitting 'c' as soon as you
see libreboot's grub menu and try:

grub> ls

the ls will hang for 2-3 minutes while something trying access to the
ahci1 (i.e., usually the DVD device) times out.

You can avoid this problem by making sure you use a grub.cfg for your
libreboot that does not try to touch ahci1 during boot.  Francis just
made this commit:
   
https://notabug.org/fchmmr/libreboot/commit/7b3449e35aa99310d4f247952a1e4fbd8f76ef2e

which I think is a mistake; actually, I think there should be another
menu option called
  "Try to boot only from (ahci0) (when faulty DVD drives are included)"
  that does something similar.


Francis has identified that this is ultimately an upstream GRUB issue,
but this Debian bug report:
   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=558661

for a similar issue indicates that it's actually a BIOS bug, not a GRUB
bug (which would mean, in this case, it's libreboot's bug :)  I posted
on that bug ticket for posterity.

Also, Just in case this is definitely an upstream GRUB bug, I filed it
here: https://savannah.gnu.org/bugs/index.php?47374

I don't expect further discussion or resolution on this at this time;
I'm posting only to identify the issue for the mailing list archives and
to follow up on this existing thread.  Again, the work-around is make
sure your default grub.cfg used by libreboot doesn't try to touch the
ahci assigned to the problematic DVD/CDROM drive.  (Or wait a long time
for your reboots, of course, that's always any option. ;)
-- 
   -- bkuhn
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