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Can't override video resolution with i915 using kprm[solved]
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beguiledfoil
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PostPosted: Wed Feb 28, 2018 8:32 am    Post subject: Can't override video resolution with i915 using kprm[solved] Reply with quote

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.


Last edited by beguiledfoil on Thu Mar 01, 2018 5:27 am; edited 1 time in total
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beguiledfoil
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Joined: 23 Jan 2011
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PostPosted: Thu Mar 01, 2018 5:04 am    Post subject: Reply with quote

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:

Code:
[   18.671127] [drm:drm_mode_debug_printmodeline] Modeline 61:"1920x1200" 0 193153 1920 2048 2256 2592 1200 1201 1204 1242 0x20 0x6
[   18.671130] [drm:drm_mode_prune_invalid] Not using 1920x1200 mode: VIRTUAL_X


I am now workig on understanding what VIRTUAL_X means.
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beguiledfoil
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PostPosted: Thu Mar 01, 2018 5:26 am    Post subject: Reply with quote

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 :)
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beguiledfoil
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PostPosted: Sat Apr 07, 2018 9:29 pm    Post subject: Reply with quote

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.
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