Linux issues on iMac

# Linux issues on iMac I have Ubuntu 18.04.4 LTS and Arch Linux installed on an iMac, which I think doesn't support KMS. I have gotten Ubuntu to work with several desktops, window managers, and display managers. When I attempted to install Manjaro, nothing worked, even with nomodeset, so I tried Arch. I have gotten the TTYs to work on Arch, but not X (I haven't tried Wayland yet). The problems I have had so far: - Booting without nomodeset results in a black unresponsive screen - I can't successfully startx or xinit on Arch even with nomodeset - Suspending in Ubuntu results in a black unresponsive screen - Ubuntu brightness keys don't work, but an image on the screen says it does I have a bunch of information, please let me know if any is unnecessary, or if I need to add more details. ## More boot info When I boot without nomodeset I see some info ending with the following:

*Error* No UMS support in radeon module!

At this point, the resolution sharpens slightly, then the screen goes black. With nomodeset, the screen doesn't go black but shows more logs, then proceeds to the login screen. UPDATE: I used to be able to see that message, but I can't seem to bring it back. Everything else is the same, though. ## Ubuntu 18.04 System info (as found in settings GUI): - Memory: 3.8 GiB - Processor: Intel® Core™️ i3 CPU 540 @ 3.07GHz x 4 - Graphics: llvmpipe (LLVM 9.0, 128 bits) - GNOME: 3.28.2 - OS type: 64-bit - Disk: 376.9 GB lspci | grep VGA prints 01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV730/M96-XT [Mobility Radeon HD 4670] cat /var/log/Xorg.0.log prints a whole bunch of stuff, let me know if you need any of it. ## Arch startx & prints:

X.Org X Server 1.20.8
X Protocol Version 11, Revision 0
Build Operating System: Linux Arch Linux
Current Operating System: Linux amc-arch 5.6.5-arch3-1 #1 SMP PREEMPT Sun, 19, Apr 2-2- 13:14:25 +0000 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-linux root=/dev/sda3 nomodeset
Build Date: 30 March 2020 05:05:45AM

Current version of pixman: 0.38.4
        before reporting problems, check http://wiki.x.org 
        to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
        (++) from command line, (!!) notice, (II) informational,
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file:"/var/log/Xorg.0.log", Time: Mon Apr 20 19:53:22 2020
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
ile at "/var/log/Xorg.0.log" for additional information.(EE) (EE) Server terminated with error (1). Closing log file.
xinit: giving up
xinit: unable to connect to X server: Connection refused
xinit: server error
Job 1, 'startx &' has ended

The log file is smaller, but still big. Let me know if it is necessary. # KMS - Kernel Mode Setting I have looked around the internet, and I believe the issue is kernel mode setting. If you know about this, I would appreciate help. Is the only solution an external graphics card that supports KMS? Can I use or make a window manager or desktop environment that doesn't require KMS? Can I make a suggestion to the Linux Kernel to make an alternative to KMS that will still work? Why does Ubuntu work (mostly) but Manjaro doesn't?