> One thing jumped out between the early (working) and late (broken) logs: in the
> broken ones there's no line for the fbcon loading & initializing.  Which would
> leave your display blank if/until X starts.  Maybe that's missing from the load
> in the late case?

Indeed, I discussed that with our initramfs/boot guru. So that's not a concern here.

> Ugh, ok so it's probably not a pipe underrun then if it kills the whole machine
(at least I hope not); could be a kernel panic.  You could try netconsole

Thanks for the netconsole hint, that worked beautifully. Indeed it catches a nice trace in the watermark updating:

[  489.298734] BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
[  489.298908] IP: [<ffffffffa030f1af>] intel_update_watermarks+0xcf/0xd40 [i915]
[  489.299056] PGD 0 
[  489.299152] Oops: 0000 [#1] SMP 
[  489.299289] last sysfs file: /sys/devices/pci0000:00/0000:00:02.0/drm/card0/dev
[  489.299384] CPU 0 
[  489.299481] Modules linked in: i915(+) drm netconsole i2c_algo_bit configfs snd_hda_codec_idt snd_hda_intel snd_hda_codec snd_pcm_oss snd_mixer_oss snd_pcm arc4 joydev ecb snd_seq_dummy snd_seq_oss snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq snd_timer iwl3945 iwlcore iTCO_wdt iTCO_vendor_support snd_seq_device mac80211 led_class snd psmouse dell_wmi dell_laptop cfg80211 soundcore snd_page_alloc usb_storage usbhid serio_raw dcdbas video output tg3 fbcon tileblit font bitblit softcursor intel_agp [last unloaded: drm]
[  489.300005] Pid: 2208, comm: work_for_cpu Not tainted 2.6.31-1-generic #14-Ubuntu Latitude D430                   
[  489.300005] RIP: 0010:[<ffffffffa030f1af>]  [<ffffffffa030f1af>] intel_update_watermarks+0xcf/0xd40 [i915]
[  489.300005] RSP: 0018:ffff8800229e98b0  EFLAGS: 00010202
[  489.300005] RAX: 0000000000000000 RBX: ffff880022966800 RCX: ffffffffa03244fb
[  489.300005] RDX: ffffffffa0321a20 RSI: ffffffffa0324518 RDI: 0000000000000001
[  489.300005] RBP: ffff8800229e9930 R08: 0000000000000000 R09: 000000000001a400
[  489.300005] R10: 0000000000000500 R11: 0000000000000000 R12: ffff880022967000
[  489.300005] R13: 000000000001a400 R14: ffff8800229674a0 R15: 0000000000000001
[  489.300005] FS:  0000000000000000(0000) GS:ffff8800019b4000(0000) knlGS:0000000000000000
[  489.300005] CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
[  489.300005] CR2: 0000000000000038 CR3: 0000000001001000 CR4: 00000000000006b0
[  489.300005] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  489.300005] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  489.300005] Process work_for_cpu (pid: 2208, threadinfo ffff8800229e8000, task ffff88003d5416b0)
[  489.300005] Stack:
[  489.300005]  ffff8800229e9910 ffffffffa0317a5a ffff000100000038 ffff8800229e98f0
[  489.300005] <0> ffff000100010038 ffff8800229e98e0 0000000000000001 0000000000000002
[  489.300005] <0> ffff8800229e0009 0000000000000000 ffff8800229e9920 ffff880022f3b000
[  489.300005] Call Trace:
[  489.300005]  [<ffffffffa0317a5a>] ? intel_sdvo_read_byte+0x6a/0xc0 [i915]
[  489.300005]  [<ffffffffa031161c>] intel_crtc_dpms+0xb0c/0xef0 [i915]
[  489.300005]  [<ffffffffa0317cff>] ? intel_sdvo_set_active_outputs+0x2f/0x40 [i915]
[  489.300005]  [<ffffffffa031baab>] ? intel_tv_mode_find+0x2b/0x50 [i915]
[  489.300005]  [<ffffffffa030ee52>] intel_crtc_prepare+0x12/0x20 [i915]
[  489.300005]  [<ffffffffa02dbff2>] drm_crtc_helper_set_mode+0x272/0x3d0 [drm]
[  489.300005]  [<ffffffffa03138c6>] intel_get_load_detect_pipe+0x116/0x160 [i915]
[  489.300005]  [<ffffffffa031cede>] intel_tv_detect+0x7e/0x100 [i915]
[  489.300005]  [<ffffffffa02dc273>] drm_helper_probe_single_connector_modes+0x93/0x2b0 [drm]
[  489.300005]  [<ffffffffa02dc4d6>] drm_helper_probe_connector_modes+0x46/0x80 [drm]
[  489.300005]  [<ffffffffa02dd2f8>] drm_helper_initial_config+0x28/0xc0 [drm]
[  489.300005]  [<ffffffffa0301b78>] i915_driver_load+0xc68/0xd70 [i915]
[  489.300005]  [<ffffffffa02d38b7>] drm_get_dev+0x147/0x2a0 [drm]
[  489.300005]  [<ffffffff8106c2d0>] ? do_work_for_cpu+0x0/0x30
[  489.300005]  [<ffffffffa0320bfa>] i915_pci_probe+0x10/0xd0 [i915]
[  489.300005]  [<ffffffff81280882>] local_pci_probe+0x12/0x20
[  489.300005]  [<ffffffff8106c2e3>] do_work_for_cpu+0x13/0x30
[  489.300005]  [<ffffffff81070a26>] kthread+0x96/0xa0
[  489.300005]  [<ffffffff8101308a>] child_rip+0xa/0x20
[  489.300005]  [<ffffffff81070990>] ? kthread+0x0/0xa0
[  489.300005]  [<ffffffff81013080>] ? child_rip+0x0/0x20
[  489.300005] Code: c2 20 1a 32 a0 48 c7 c6 18 45 32 a0 bf 01 00 00 00 31 c0 e8 c4 40 fc ff 4c 63 6b 74 4d 89 e9 48 8b 43 20 41 83 c7 01 44 8b 53 78 <8b> 40 38 8d 48 07 85 c0 0f 49 c8 48 8b 43 08 c1 f9 03 48 8d 58 
[  489.300005] RIP  [<ffffffffa030f1af>] intel_update_watermarks+0xcf/0xd40 [i915]
[  489.300005]  RSP <ffff8800229e98b0>
[  489.300005] CR2: 0000000000000038
[  489.308329] ---[ end trace 26bde7aeab46e24b ]---