Can't override video resolution with i915 using kprm[solved]

beguiledfoil · n00b Joined: 23 Jan 2011 Posts: 48

After updating (didn't note from which kernel, unfortunately) to 4.15 I can no longer force my external monitor's resolution via the video kernel parameter. If I try to do so I get a black screen on the external monitor.

video=DP-1=1920x1200D is the command I am trying. I *believe* that my monitor is providing a bad edid (it is pretty old), and up until this point overriding the video parameter was the only way to get a correct resolution. Note that I am not using X.

I am making some progress and will post more in this thread as I find it.

beguiledfoil · n00b Joined: 23 Jan 2011 Posts: 48

First, I have found this kernel patch:

https://patchwork.kernel.org/patch/10114651/

I have applied it. Next I have started running with drm.debug=0x1e kernel parameter.

I now have several logs. The most relevant part of the logs, from a boot with a video override:

beguiledfoil · n00b Joined: 23 Jan 2011 Posts: 48

I have found a workaround. I have not tested it exhaustively, but I am typing from an instance of Chrome at full resolution, so...

Intel fbdev appears to be incapable of allocating "planes" larger than the initial allocation. So using the kernel parameters "video=DP-1:1920x1200e video=eDP-1:1920x1200D" gets my second monitor to display correctly. The laptop screen (eDP-1) renders text at an absurdly small size, but I can start sway and everything resizes to proper resolutions. Again, this may be some fallout from bad edids from my old Samsung Syncmaster 2443bw.

I will try to make a formal bug report when I have time. If anyone else runs in to this issue please post here

beguiledfoil · n00b Joined: 23 Jan 2011 Posts: 48

As of 4.16.0 my "fix" no longer works. I have resumed investigations.

Edit: to clarify setting a custom video parameter for the laptop screen results in a freeze at boot.