[Bug 98523] Can't run without "nomodeset" on MacPro6,1 with two AMD R9 280X Tahiti video cards

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98523

--- Comment #1 from Heigh <Heigh.Leigh171 at gmail.com> ---

Hi Michel,

Thank you for looking into this, and for assigning the bug.

In the meantime, I have found a workaround or a solution.

The system needs to be booted with systemd-boot bootloader
(or perhaps any other supporting UEFI boot)

When I boot Ubuntu with standard, installed during installation
grub2, radeon driver would't detect external displays connected via
Display Ports.

But when I boot system using systemd-boot installed by Arch Linux (or KaOS),
it detects displays normally, and works correctly, supporting
all external displays as expected.

I think this is related to some aspects of the hardware not
exposed in BIOS boot mode, and exposed in EFI/UEFI boot mode.

Preferred solution would be working radeon driver in BIOS mode
if possible, or, if that is not possible, some meaningful message 
in the system journal explaining that certain features 
(e.g. external monitors via Display Port) will not be supported 
unless the system is booted in EFI/UEFI mode.

Thank you,
Heigh

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