Maybe someone knows if alphanumeric mode setup is via the standard VGA register set on most modern VGA cards.
I am afraid your are wrong. For modern VGA cards, there is actually no alphanumeric mode. These alphanumeric mode were simulated by BIOS or drivers. The worst thing, if you have no documents about these extended registers, you have no way to drive the clock gen for Dot clock, Hsync, Vsync.
Are you saying that it is not possible to use a text console with Linux (vgacon.c) with modern VGA cards (BIOS mode 3)? Only framebuffer? Or are you saying that without extra information (ie, the BIOS or the manuals) you can't init it into mode 3? I don't understand your answer.
I thought most vga cards were register compatible with the legacy VGA register set, only that there were a lot of other (sometimes secret) things to setup. Is this wrong?
Fortunately regular vga cards are not very important to me, actually, I am really most interested in integrated chipsets, such as the stpc and the via apollo ple133 northbridge, both of which are legacy VGA register compatible. They have a lot of other registers to setup, of course, but at least the problem is reduced if you have the standard register setup code already done. And of course the documentation is complete and not a secret. I am only interested in text mode right now.
-Steve