F22 unusable - system freezes on login

[Matthew Woehlke]

I recently installed F22 (KDE spin) from scratch on a new Dell M6800.
The Live CD seems to run okay, but when I try to boot the installed OS,
it freezes when I try to log in. The machine is effectively unusable as
a result.

Through much pain and anguish I have managed to install updates (up to
date as of earlier today), to no effect.

This affects login regardless of the method: graphical, tty, ssh,
running 'login' from an emergency shell. If I'm lucky, TTY switching
still works, but any login attempt hangs, and some take the whole system
out. Only booting in emergency/maintenance/single mode works.

My /var/log/messages is corrupt and contains no useful information.
/var/log/boot.log has nothing obvious. The only potential clue I've seen
is in dmesg:

  snd_hda_intel 0000:01:00.1: Enabling via VGA-switcheroo
  snd_hda_intel 0000:01:00.1: CORB reset timeout#2, CORBRP = 65535

The internet has some suggestions¹ that this may be the problem. There
are references to adding "options snd-hda-intel enable=0,1,0" to a
configuration file, but the file referenced does not exist.

(¹ See https://bbs.archlinux.org/viewtopic.php?pid=1460933 for example.)

Any ideas? Unfortunately it's near impossible to diagnose this because I
can't have a usable shell while tickling the issue.

-- 
Matthew