My bootloader (syslinux) leaves the screen in 80×25 text mode. I have no fbcon module loaded, only i915. Then Xorg starts with lightdm greeter, my screen's resolution appears to be 640×480, but Xorg thinks it is 1024×600 ("xrandr --current" says so). I can only see top left corner of the picture. When I move my mouse to the right edge of the screen, flickering starts until I return my mouse back. If I boot without i915.fastboot=1, native resolution 1024×600 is set. So the issue is that with i915.fastboot=1 real resolution set (640×480) differs from the one reported by driver (1024×600).
Please set drm.debug=14 module parameter, and attach dmesg from boot to the problem (flickering with mouse movement).
Created attachment 165841 [details] dmesg.log I booted, Xorg started, I waited several seconds, moved the mouse to right edge of the screen, image started to flicker, I waited several seconds, returned mouse back, image finished flickering, I waited several seconds, then switched to tty1, logged in as root (blindly, as fbcon module was not loaded), modprobed fbcon and saved dmesg. The main problem is not flickering, it is wrong resolution reported. Actually screen shows 640×480, but driver reports it as 1024×600, so both in Xorg and fbcon I can only see top left corner of the picture.
The resolution is definitely set to 1024x768, but we leave pfit enabled with a source size of 640x480 as the fastboot hack prevents the full mode switch in this instance.
(In reply to Chris Wilson from comment #3) > The resolution is definitely set to 1024x768, but we leave pfit enabled with > a source size of 640x480 as the fastboot hack prevents the full mode switch > in this instance. Sorry, you probably meant 1024×600, it's a laptop (MSI Wind U100), it doesn't support 1024×768.
Related to http://patchwork.freedesktop.org/patch/36598 I presume.
The fastboot option is gone since commit 6764e9f8724f1231b4deac53b9a82286ac0830e7 Author: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> Date: Thu Aug 27 15:44:06 2015 +0200 drm/i915: skip modeset if compatible for everyone. Please file any new bug reports at the freedesktop.org bugzilla [1]. Thank you. [1] https://bugs.freedesktop.org/enter_bug.cgi?product=DRI&component=DRM/Intel