Librem Mini 2 only 30Hz on 4k DP

PureOS
#1

Dear Purism Community

I bought a Librem Mini 2 with Pureboot bundle to use as media center. Unfortunately, it doesn’t work as expected. On Wayland I had to use a small display to be able to see any output during boot. E.g. when having to enter the pin for Pureboot. After boot, I was able to connect the 4k TV, however everything lagged. Even the mouse was really slow, not to mention playing any movies.

Disabling Wayland and switching to XServer, solved the boot problem somewhat. With the 4k TV connected, I can now see output during boot and I’m now able to enter the pin for Pureboot. However, at 4k resolution, I only get a maximum refresh rate of 30Hz:

$ xrandr 
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 16384 x 16384
DP-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 1600mm x 900mm
   4096x2160     30.00    25.00    24.00    29.97    23.98  
   3840x2160     30.00    25.00    24.00    29.97    23.98  
   1920x1080    120.00*  100.00   119.88    60.00    50.00    59.94    30.00    25.00    24.00    29.97    23.98  
   1920x1080i    60.00    50.00    59.94  
   1280x1024     60.02  
   1360x768      60.02  
   1280x720      60.00    50.00    59.94  
   1024x768      60.00  
   800x600       60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       60.00    59.94  
   720x400       70.08  
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 disconnected (normal left inverted right x axis y axis)
HDMI-2 disconnected (normal left inverted right x axis y axis)

I just bought a high-end cable (DP -> HDMI), so I doubt that the cable is the issue. I also tried the HDMI output. Same results. The TV is a fairly new LG OLED TV which I have tested with several devices with 4k output.

It seems that this is a firmware issue. As the Intel UHD Graphics 620 should support 4k@60Hz. Also, other users seem to have a working setup [1]. However, maybe they don’t use Pureboot?

Any thoughts, hints, or workarounds? I don’t have a use for the device other than use it as media center…

Cheers,
Anton

[1] Librem Mini 2 No HDMI Signal

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#2

Did you try via HDMI cable (not DP-HDMI)? I have no problems with my LG TV (4K@60Hz) with common HDMI cable.

#3

@mladen thank you for your suggestion. I just tried that again. No output at all.

Debugging via ssh:

$ xrandr -display :0.0 -q
Screen 0: minimum 320 x 200, current 4096 x 2160, maximum 16384 x 16384
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 connected primary 4096x2160+0+0 (normal left inverted right x axis y axis) 1600mm x 900mm
   4096x2160     30.00*   25.00    24.00    29.97    23.98  
   3840x2160     30.00    25.00    24.00    29.97    23.98  
   1920x1080    120.00   100.00   119.88    60.00    50.00    59.94    30.00    25.00    24.00    29.97    23.98  
   1920x1080i    60.00    50.00    59.94  
   1280x1024     60.02  
   1360x768      60.02  
   1280x720      60.00    50.00    59.94  
   1024x768      60.00  
   800x600       60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       60.00    59.94  
   720x400       70.08  
DP-3 disconnected (normal left inverted right x axis y axis)
HDMI-2 disconnected (normal left inverted right x axis y axis)

What’s weird is that even though I connected the TV via HDMI, xrandr still claims that DP-2 is connected… However, the refresh rate is still at 30Hz.

@mladen I’m curious, what is your setup? Are you at 4096x2160 or 3840x2160 resolution?

#4

To get 4K@60 video over DisplayPort, you need a cable that can use all 4 DP lane pairs. If you are using a DP->HDMI adapter cable, you may only be getting 2 lane pairs, which will give you a max of 4k@30Hz video. You may want to try a cable that advertises that it supports 4k@60.

#5

I am not using my TV everyday with my Mini, only when I test something, but I can check. What I noticed is that you need to have HDMI cable plugged in before starting the Mini.

Also please try what amosbatto suggested.

#6

Thank you @amosbatto, the cable in question [1] does advertise 4K@60.

In my other test I used a HDMI cable of a device that has no problem with 4K@60. But with this setup I get different results [2], even when having the cable plugged in during boot.

[1] https://www.digitec.ch/en/s1/product/roline-displayport-hdmi-4k-2m-hdmi-display-port-video-cables-11615151
[2] Librem Mini 2 only 30Hz on 4k DP

#7

@mladen or @amosbatto do you guys have by any chance Pureboot enabled? I have a feeling that this could have an effect on the GPU. As far as I understand, Pureboot has its own Linux kernel which then kexecs to the PureOs kernel. Maybe there is something wrong with the hand-off…

If you in fact use Pureboot as well, and are able to do 4K@60, it would prove my assumption wrong.

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#8

I only tested with coreboot so far, I will need some time to install PureBoot.

1 Like