[OpenBIOS] Video

[Jeff Garzik]

"Ronald G. Minnich" wrote:
> the thing is, as long as you depend on vga bios support, you're never
> going to be openbios. One reason is that graphics are increasingly a chip
> on the motherboard, with the vga bios in the motherboard nvram. There
> isn't room for linux and that vga bios in the nvram. Second is, until you
> get all the secrets out, we're locked in to braindead bios'es.

I agree with you!  :)


> So we'll figure it out :-)

VGA is the standard, that is why it is popular.  Linux text mode console
works because VGA works on most PCs.  Executing video BIOS is an
absolute requirement to supporting VGA in a generic fashion.


WARNING:  You are opening a huge can of worms if you ditch VGA and video
BIOS.  I think it is a good idea, but it is difficult to implement.  I
know, I've written graphics drivers.


If you do NOT want to support VGA in a generic fashion, then you MUST
include specific support for each graphics chipset your users may have. 
Those are the only two options.

Some video cards include Open Firmware ROMs.  This is the
platform-independent way of initializing the video card.  Open Firmware
ROM code is somewhat like forth, from what I've heard.

For video cards without Open Firmware support, you need to get the video
card datasheet and figure out how to initialize the card.  You must do
this for each model of each card.  Sometimes initializing to text mode
is easy, sometimes not.

This task is further complicated by the fact that _many_ video cards
invest a lot of tech in their video BIOS's.  BIOS stores critical
undocumented RAM timing information and similar board details which
differ from board to board, but not chip to chip.  Usually you can get
away with 100% conservative video settings, but this is not failsafe.

Once you have code to initialize popular video cards to a sane state,
you can start using linuxbios on different computers...

As i said, ditching VGA and video BIOS is a very good thing.  But it is
also difficult to get right, and requires lots of additional code over
the simply-support-VGA-the-old-way solution.

Choose well, grasshopper.  :)

-- 
Jeff Garzik         | Writing software is
Building 1024       | more fun than working.
MandrakeSoft, Inc.  | 	-Anon
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