I am not sure why, but on my system, I get the following warning on every boot:

/var/log/kernel/warnings.log
Jun 25 19:09:57 localhost kernel: ------------[ cut here ]------------
Jun 25 19:09:57 localhost kernel: WARNING: at drivers/gpu/drm/i915/intel_dp.c:410 intel_dp_aux_ch+0x139/0x4f0 [i915]()
Jun 25 19:09:57 localhost kernel: Hardware name:         
Jun 25 19:09:57 localhost kernel: dp_aux_ch not started status 0x0143003f
Jun 25 19:09:57 localhost kernel: Modules linked in: i915(+) video drm_kms_helper drm i2c_algo_bit ipv6 xfs ide_pci_generic ide_core usb_st
orage snd_hda_codec_hdmi snd_hda_codec_realtek fglrx(PO) joydev coretemp kvm_intel kvm iTCO_wdt iTCO_vendor_support gpio_ich hid_generic cr
c32c_intel ghash_clmulni_intel aesni_intel aes_x86_64 xts lrw gf128mul ablk_helper cryptd i2c_i801 i2c_core snd_hda_intel serio_raw snd_hda
_codec snd_hwdep snd_pcm amd_iommu_v2 e1000e lpc_ich snd_page_alloc cpufreq_ondemand snd_timer cpufreq_conservative cpufreq_powersave snd m
ei soundcore ata_generic tpm_tis acpi_cpufreq tpm mperf tpm_bios processor evdev usbhid hid nfsd exportfs auth_rpcgss nfs_acl lockd sunrpc 
autofs4 xhci_hcd ehci_pci ehci_hcd usbcore firewire_ohci firewire_core crc_itu_t usb_common button dm_mirror dm_region_hash dm_log dm_mod p
ata_acpi [last unloaded: microcode]
Jun 25 19:09:57 localhost kernel: Pid: 1138, comm: upowerd Tainted: P           O 3.8.13-desktop-1.mga3 #1
Jun 25 19:09:57 localhost kernel: Call Trace:
Jun 25 19:09:57 localhost kernel:  [<ffffffff81055e4f>] warn_slowpath_common+0x7f/0xc0
Jun 25 19:09:57 localhost kernel:  [<ffffffff81055f46>] warn_slowpath_fmt+0x46/0x50
Jun 25 19:09:57 localhost kernel:  [<ffffffffa0cbc569>] intel_dp_aux_ch+0x139/0x4f0 [i915]
Jun 25 19:09:57 localhost kernel:  [<ffffffffa0cbc9d5>] intel_dp_aux_native_read_retry+0xb5/0x140 [i915]
Jun 25 19:09:57 localhost kernel:  [<ffffffffa0cbd491>] intel_dp_get_dpcd+0x21/0x70 [i915]
Jun 25 19:09:57 localhost kernel:  [<ffffffffa0cbd4fd>] intel_dp_detect_dpcd+0x1d/0x100 [i915]
Jun 25 19:09:57 localhost kernel:  [<ffffffffa0cbe367>] intel_dp_detect+0x77/0x2d0 [i915]
Jun 25 19:09:57 localhost kernel:  [<ffffffffa0c48c36>] status_show+0x46/0x90 [drm]
Jun 25 19:09:57 localhost kernel:  [<ffffffff81435030>] dev_attr_show+0x20/0x60
Jun 25 19:09:57 localhost kernel:  [<ffffffff8112018e>] ? __get_free_pages+0xe/0x50
Jun 25 19:09:57 localhost kernel:  [<ffffffff811ebd85>] sysfs_read_file+0xa5/0x1c0
Jun 25 19:09:57 localhost kernel:  [<ffffffff811781d9>] vfs_read+0xa9/0x180
Jun 25 19:09:57 localhost kernel:  [<ffffffff81178302>] sys_read+0x52/0xa0
Jun 25 19:09:57 localhost kernel:  [<ffffffff815e0fed>] system_call_fastpath+0x1a/0x1f
Jun 25 19:09:57 localhost kernel: ---[ end trace 28fedb5926eddf2d ]---
Jun 25 19:09:57 localhost kernel: i915: No ACPI video bus found


This is a muliseat setup, so I have both an intel graphics card and an ATI graphs card.  They both mostly work.