Re: Calling VESA BIOS routines from kernel?

Khimenko Victor (khim@sch57.msk.ru)
Sun, 12 Dec 1999 22:24:03 +0300 (MSK)

In <199912121804.KAA24523@adam.yggdrasil.com> Adam J. Richter (adam@yggdrasil.com) wrote:
> I am contemplating the idea of implementing support in the
> kernel for calling the VESA video BIOS routines for reading DDC
> timing information from the monitor (to improve autoconfiguration of
> the X window system and svgalib). I see that the kernel APM support
> appears to do something like this, but my naive attempt to do something
> similar with the DDC calls resulted in a kernel panic.

> So, I am wondering: are the APM calls special in that they
> can still work even though the kernel has already thoroughly messed
> with the hardware, put the process into 32-bit protected mode, and
> so on, or are all VESA BIOS extensions generally supposed to support
> being called from a 32-bit protected mode operating system (i.e., is there
> hope for this approach, or do I have to try to hack the boot loader)?

APM is special (or rather it SHOULD BE special: a lot of screwed implementations
out there still expect that you'll call them only from real mode). VESA calls
are not (that's why XFree86 4.0 must emulate real mode enviroronment and
why recently was thread about problems with that emulation). As XFree86 4.0
will emulate real time environment for multihead anyway I guess you'll be
able to add DCC support there easily. Not sure about svgalib, though...

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