Description of problem: The screen of my Dell Latitude 7480 laptop is flickering. The issue does not occur when the laptop is connected to an external display (via a Dell WD 15 docking station using a USB-C/DisplayPort connection). The issue started to appear after a BIOS update (applied via Windows 10 on August 3 2017; new BIOS version is 1.5.2). The system was working without problems for about one month before that. Not sure if related, but the changelog of the BIOS update lists "Updated Processor Microcode" as one item. I assume this is not an xorg but rather a kernel driver issue, since it also occurs when I am in a terminal (i.e. without X-server). Workaround: When setting the kernel boot parameter i915.enable_rc6=0 the screen is not flickering and everything works as expected. Version-Release number of selected component: Processor: Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz GPU: Intel(R) HD Graphics 620 (Kaby Lake GT2) Kernel: 4.11.11-300.fc26.x86_64 libdrm: 2.4.82-1.fc26 Mesa: 17.1.5-1.fc26 Desktop environment: KDE Frameworks 5.36.0 How reproducible: Simply boot the laptop (without an external display), the flickering is immediately visible when the login screen shows up or in a terminal session (i.e. without X-server). Possibly related bugs: https://bugzilla.redhat.com/show_bug.cgi?id=1353664 https://bugzilla.redhat.com/show_bug.cgi?id=1353008 https://bugzilla.redhat.com/show_bug.cgi?id=1354129
I found this error message in the log (dmesg) in cases when the flickering occurs: [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun When setting the kernel boot parameter i915.enable_rc6=0 this error does not occur and the screen is not flickering. Not entirely sure if it is relevant to this bug, but it very much seems so.
I confirm the same issue with F26 + Cinnamon desktop. Option "i915.enable_rc6=0" seems to workaround the issue. $ dmesg |grep 915 [ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.11.11-300.fc26.x86_64 root=UUID=a36ad57f-055e-410f-9758-848bad1a2169 ro i915.enable_rc6=0 rhgb quiet [ 0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.11.11-300.fc26.x86_64 root=UUID=a36ad57f-055e-410f-9758-848bad1a2169 ro i915.enable_rc6=0 rhgb quiet [ 3.139155] ACPI: Power Resource [LPP] (on) [ 3.889150] AES CTR mode by8 optimization enabled [ 4.730391] i915 0000:00:02.0: vgaarb: changed VGA decodes: olddecodes=io+mem,decodes=none:owns=io+mem [ 5.876895] [drm] Initialized i915 1.6.0 20170123 for 0000:00:02.0 on minor 1 [ 7.037151] i915 0000:00:02.0: fb0: inteldrmfb frame buffer device [ 8.212754] snd_hda_intel 0000:00:03.0: bound 0000:00:02.0 (ops i915_audio_component_bind_ops [i915]) $ lspci | grep VGA 00:02.0 VGA compatible controller: Intel Corporation HD Graphics 5500 (rev 09) 04:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Opal PRO [Radeon R7 M260] (rev ff) $ uname -a Linux localhost 4.11.11-300.fc26.x86_64 #1 SMP Mon Jul 17 16:32:11 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
We apologize for the inconvenience. There is a large number of bugs to go through and several of them have gone stale. The kernel moves very fast so bugs may get fixed as part of a kernel update. Due to this, we are doing a mass bug update across all of the Fedora 26 kernel bugs. Fedora 26 has now been rebased to 4.15.4-200.fc26. Please test this kernel update (or newer) and let us know if you issue has been resolved or if it is still present with the newer kernel. If you have moved on to Fedora 27, and are still experiencing this issue, please change the version to Fedora 27. If you experience different issues, please open a new bug report for those.
> Fedora 26 has now been rebased to 4.15.4-200.fc26. Please test this kernel > update (or newer) and let us know if you issue has been resolved or if it is > still present with the newer kernel. As mentioned earlier, setting the kernel boot parameter 'i915.enable_rc6=0' circumvented the issue, and I have been using this workaround ever since I reported the bug. In response to this, I have tested booting without this parameter explicitly set and everything seems to be fine. I also checked the options for the i915 module, and it appears that the rc6 options is explicitly set to 1 now (the default is -1, and I don't set it explicitly anywhere): # cat /sys/class/drm/card0/power/rc6_enable 1 I am closing this issue thus.