Description of problem:

machine is a lenovo x1 carbon ultrabook connected to an external display via mini-DP-to-vga-adapter.

adapter was connected to the machine, then the machine was powered up.
the machine failed to properly initialize the display (display was black with the screen indicator light flashing error). unplugging the adapter and plugging it back in works around the issue.

the following was found in dmesg:
[   21.332031] ------------[ cut here ]------------
[   21.332061] WARNING: CPU: 2 PID: 811 at drivers/gpu/drm/i915/intel_dp.c:2747 intel_dp_link_down+0x1d2/0x210 [i915]()
[   21.332062] Modules linked in: ip6table_filter ip6_tables ebtable_nat ebtables bnep iTCO_wdt iTCO_vendor_support vfat fat snd_hda_codec_hdmi x86_pkg_temp_thermal coretemp snd_hda_codec_realtek kvm_intel snd_hda_intel snd_hda_codec snd_hwdep kvm arc4 crct10dif_pclmul crc32_pclmul crc32c_intel iwldvm snd_seq mac80211 ghash_clmulni_intel snd_seq_device microcode snd_pcm serio_raw iwlwifi i2c_i801 cfg80211 sdhci_pci sdhci mmc_core lpc_ich btusb mfd_core bluetooth cdc_ether usbnet mii hid_multitouch joydev shpchp mei_me snd_page_alloc snd_timer mei wmi thinkpad_acpi snd soundcore rfkill binfmt_misc i915 i2c_algo_bit drm_kms_helper drm i2c_core video
[   21.332095] CPU: 2 PID: 811 Comm: Xorg Not tainted 3.13.6-200.fc20.x86_64 #1
[   21.332096] Hardware name: LENOVO 3448B86/3448B86, BIOS G6ET96WW (2.56 ) 04/29/2013
[   21.332098]  0000000000000009 ffff8800d2e05c08 ffffffff8168730c 0000000000000000
[   21.332101]  ffff8800d2e05c40 ffffffff8106d47d ffff88020ff1d8c8 ffff88020ff1c800
[   21.332104]  ffff8802126d7000 0000000080080304 ffff88020ffd8000 ffff8800d2e05c50
[   21.332107] Call Trace:
[   21.332113]  [<ffffffff8168730c>] dump_stack+0x45/0x56
[   21.332118]  [<ffffffff8106d47d>] warn_slowpath_common+0x7d/0xa0
[   21.332121]  [<ffffffff8106d55a>] warn_slowpath_null+0x1a/0x20
[   21.332139]  [<ffffffffa00d28a2>] intel_dp_link_down+0x1d2/0x210 [i915]
[   21.332156]  [<ffffffffa00d6be0>] intel_disable_dp+0x70/0x80 [i915]
[   21.332170]  [<ffffffffa00bb51e>] ironlake_crtc_disable+0x1ae/0x940 [i915]
[   21.332185]  [<ffffffffa00c1adf>] intel_crtc_update_dpms+0x6f/0xa0 [i915]
[   21.332199]  [<ffffffffa00c5449>] intel_connector_dpms+0x59/0x70 [i915]
[   21.332211]  [<ffffffffa00303f8>] drm_mode_obj_set_property_ioctl+0x328/0x340 [drm]
[   21.332220]  [<ffffffffa0030440>] drm_mode_connector_property_set_ioctl+0x30/0x40 [drm]
[   21.332227]  [<ffffffffa001fb52>] drm_ioctl+0x502/0x630 [drm]
[   21.332232]  [<ffffffff8156aef1>] ? sock_aio_read+0x21/0x40
[   21.332235]  [<ffffffff811b834a>] ? do_sync_read+0x5a/0x90
[   21.332238]  [<ffffffff811cb758>] do_vfs_ioctl+0x2d8/0x4a0
[   21.332241]  [<ffffffff811b8a0e>] ? vfs_read+0xee/0x160
[   21.332243]  [<ffffffff811cb9a1>] SyS_ioctl+0x81/0xa0
[   21.332247]  [<ffffffff816962e9>] system_call_fastpath+0x16/0x1b
[   21.332248] ---[ end trace 2ade52e0417b890e ]---


Version-Release number of selected component (if applicable):

kernel version - 3.13.6-200.fc20.x86_64 #1 SMP Fri Mar 7 17:02:28 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

How reproducible:

Steps to Reproduce:
1. power off the machine.
2. connect the screen via the display adapter
3. power on the machine.

Actual results:
nothing is displayed on external monitor (although it it still recognized as primary, as evident by GDM)

Expected results:
external display should come up properly and (as it is the primary configured display) show the GDM login screen

Additional info: