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I have been running ubuntu on an 2009 iMac for a few years. I did an upgrade from 18.04 to 20.04 and everything was fine. I have had a persistent problem with a disappearing mouse cursor and have seen suggestions that this is a video driver issue.

I tried installing an Nvidia driver based on this question but that was clearly incorrect and I could not get back to the Ubuntu desktop. I purged that driver.

Now I can get back to the desktop but I have an Unknown Display in the settings, and my resolution is 1400x1050.

Here are the specifications for my hardware. The screen should be 1920x1080.

(I also tried installing nouveau-firmware but have also purged that.)

Screenfetch details:

OS: Ubuntu 20.04 focal
Kernel: x86_64 Linux 5.4.0-144-generic
Uptime: 2h 38m
Packages: 2445
Shell: bash 5.0.17
Resolution: 1400x1050
DE: GNOME 3.36.5
WM: Mutter
WM Theme: Ambiance
GTK Theme: Yaru [GTK2/3]
Icon Theme: Yaru
Font: Ubuntu 11
Disk: 1.2T / 1.8T (66%)
CPU: Intel Core2 Duo E7600 @ 2x 3.059GHz
GPU: llvmpipe (LLVM 12.0.0, 128 bits)
RAM: 2346MiB / 7933MiB

This is what I got from lshw -C display:

*-display UNCLAIMED       
   description: VGA compatible controller
   product: RV730/M96-XT [Mobility Radeon HD 4670]
   vendor: Advanced Micro Devices, Inc. [AMD/ATI]
   physical id: 0
   bus info: pci@0000:02:00.0
   version: 00
   width: 64 bits
   clock: 33MHz
   capabilities: vga_controller bus_master cap_list
   configuration: latency=0
   resources: memory:c0000000-cfffffff memory:d0220000-d022ffff ioport:1000(size=256) memory:c0000-dffff

I have nomodeset as part of my Grub configuration.

Brandon Rickman
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1 Answers1

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I figured it out, sharing this as a public service.

I have been using nomodeset in my Grub config since I first installed 16.04 -- which was in 2016. When I upgraded to 18.04 I did not change it, and everything still worked fine.

When I upgraded to 20.04, things were still working fine until I tried to update the video driver as above. But what I really needed to do was figure out the correct Grub settings. This is what fixed it for me:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash radeon.cik_support=1 radeon.si_support=1"

(The "cik" in cik_support stands for Caribbean Island GPUs, and "sik" is Sea Islands GPUS. Those are different chipsets used by the video card, not sure which one I have but the system can figure it out.)

That is it. I'm now using the radeon driver, with a generic "Built-in display" at the full 1920 x 1080 resolution.

Brandon Rickman
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