Dear Fellow KaOS-ers,
In short:
MacPro6,1, KaOS LiveUSB successfully runs on 3 external monitors connected via DisplayPorts,
but installed system hangs with errors in boot log and black screen.
Details:
I have a rare configuration of 2016 MacPro6,1 with two AMD Radeon Tahiti video cards
and three 4-K monitors, connected via DisplayPort / Thunderbolt ports.
I came to KaOS from this thread: https://forum.kaosx.us/d/1662-kaos-install-on-macpro6-1-ati-d500/22
It says that KaOS is the only system that can use external displays on MacPro6,1 connected via DisplayPorts.
Any other distro I tried so far (various versions of Ubuntu, Mint), required nomodeset, and ran only on a monitor connected via HDMI. That was the case for both LiveUSB, and for installed system.
So, I downloaded KaOS-2016.09-x86_64.iso, and indeed, the installer was able to turn ON all three monitors,
which I've never seen on any other distro. That was amazing.
I installed the system, and it boots with black screen, and I can see errors in journalctl -b output:
Oct 25 06:42:08 macpro kernel: radeon 0000:06:00.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0x0000
Oct 25 06:42:08 macpro kernel: radeon 0000:06:00.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0x0000
I've seen exactly same errors when tried to run Ubuntu and Mint without nomodeset option.
So, I'm trying to understand, what exactly does KaOS LiveUSB do that makes radeon driver successfully detect and use external monitors, connected via DisplayPort, and how to make installed system to do same thing.
I've read many, many forums and wikis, and my understanding, that this is something to do with UEFI vs. BIOS boot mode. I read, that PCI ROM is not available in UEFI mode, see: https://bugs.freedesktop.org/show_bug.cgi?id=26891
But, KaOS LiveCD somehow manages to overcome this, while installed KaOS system doesn't.
Please provide me with some pointers / clues.
Thank you,
Heigh