"Eric W. Biederman" wrote:
> Jeremy Jackson <[EMAIL PROTECTED]> writes:
>
> > "Eric W. Biederman" wrote:
> >
> > > If you have a framebuffer driver for the video card you shouldn't need
> > > to even touch the video bios. Worst case is that you need to tweak it
> > > to actually initialize the video card from the completely unitialized
> > > state.
> >
> > why the difficulty with cirrusfb on linuxbios.org then?
> Because we were worrying about other things.
oh.
>
>
> > why does xfree86 use the video bios for multi-headed initialization?
> Beats the heck out of me. It may have been a reasonable bang for
> the buck compromise to support every card at once. But I wouldn't
> without knowing why it is safe, trust the normal BIOS to initialize a
> second head if it didn't do it during the boot up sequence. There are
pc's can only init one card via BIOS. you can set the io permission
bitmap and page protections /segment registers to protect anything
but what the video bios extension is supposed to touch (ie vid card)
>
> too many legacy i/o ports that overlap on every video card.
no only one card actually emulates an ibm VGA adapter's
registers. it's a pci config regster bit. the rest are (or all
if you clear the vga-enable bit) mapped like any other
PCI device.
>
>
> > I don't think this is trivial,
> > since video card register specs seem to be hard to get (NDA) in many cases
> > and/or the init sequence is complicated.
>
> It may not be quite trivial, but it is the direction the kernel is
> heading in. I can name at least 3 framebuffer drivers that do
> complete video card setup. And there are probably more.
I agree that's the way it *should* go. But some cards must have
NDA or complexity issues (just inferring here) that's why XF86
uses the real-mode bios to init the card. Since it appears it's
possible ( == XF86 4.0 work on *my* 3 headed machine),
kernel could use all cards with fb driver immediately with such
a technique.
I forget now why this all was so important...?
