After many attempts I have now finally succeeded in installing and booting gentoo via UEFI. The main issue I was faced with was an SAS adapter which I had crossflashed from its RAID firmware to a simple HBA firmware with adding only the BIOS rom firmware file, but missing out on the UEFI rom firmware file - but that's another story ...
Anyways, I am still struggling with an issue I seem to be unable to solve. I use grub2 to boot the system and I am also able to set the desired graphical video mode in grub. Once I have selected the boot entry and pressed the Enter-key the only thing I see on the console screen is an indication to boot the selected entry (which stems from grub2). After that the monitor does not show any messages until such time the graphics card/framebuffer kernel driver is loaded (which is around the 7 to 8 seconds mark). Only then are boot messages going to show on the console.
I have experimented with numerous combinations of framebuffers (simplefb, efi-fb, mga KMS driver for my card), grub2 settings (gfxmode, gfxpayload) and kernel settings (video=), but none appears to be able to display early boot messages:
While the desired resolutions all work both in grub and in linux, the handover from one to the other seems to stall until such time the linux kernel driver is actually activated. Around the time when the corresponding messages are shown in /var/log/dmesg, boot messages start being displayed on the console video monitor.
I am running out of ideas on how to be able to also display early boot messages on my monitor - even if they showed up in a lower resolution only.
Does a pure UEFI boot scenario (also displaying early boot messages) actually work for anybody or is this simply not possible?
Thanks Atom2

