Re: x86 - Realmode BIOS and Code calling module

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

On Iau, 2004-08-12 at 14:38, Jakub Vana wrote:
> > Why is this better than LRMI in user mode.
> 
> I was now looking on LRMI. It must be a nice code, but It is still only
>  V86 emulation. I have listen that some BIOSes use something called 
> Unreal mode, that is realmode with segment registers used like in 
> protected mode. There is only one way, how to set this segregs - 
> switch to prot. mode, but if the BIOS try to switch when is running 
> in V86 CPU generates #GP (Global Protection fault). Not if it is 
> running in real Real Mode.

I've yet to meet a video bios that does this. I don't think the X folks
have either, but you could run it past Egbert to make sure. The 
"unreal" mode is normally only in existance during early boot.
> 
> > To do BIOS calls safely
> > you need to be very careful about things like PCI locking, I/O 
> > emulation and the ROM scribbling 
> 
> I'm not sure abou this, but I think there is not problem in calling 
> BIOS, here is problem in BIOS handling with this features and so 
> It's the problem of programmer that calls the BIOS to safely work
> and synchronize his hardware in kernel with BIOS. Other hardware 
> (that is not pawn by BIOS) can't make problems.

One example is PCI configuration accesses which must be co-ordinated
with the kernel, and through the kernel PCI interfaces.