Reset and real mode
Fri, 5 Dec 2003 19:24:44 -0800 (PST)
> I've been chatting a bit with the ACPI folks; there are rumors that some
> ACPI implementations resume the machine without POSTing the video card, so
> even text-mode systems will require video support. Obviously the easiest
> code to use for that is sitting on the video card, but that will entail
> some mechanism for running real-mode code as ACPI resumes the machine.
> It may turn out that the kernel will end up supporting Int10 calls from
> protected mode much as Windows did, in which case we may want to leverage
> that for some of this functionality as well. Using "real" real-mode
> instead of vm86 will work better with video cards anyway.
I've talked with Alan Cox about making VM86 type Int10 calls from kernel mode.
It is never going to happen in Linux. It's not that they are against doing it
but the way Linux configures the x86 CPU prevents using VM86 from kernel mode.
There are three choices:
1) init secondary cards in real mode before the kernel enters protected mode.
This can be done by playing with the init time assembly code in x86/arch
2) use VM86 and all the pain that entails
3) Convince the board manufacturers to give us the code for resetting the
hardware. For example even though I have full doc for the R200 I don't have the
sequence needed to reset it. Apparently there is a BIOS kit that I don't have
since it includes source code. If we had the reset sequence it is trival to add
a reset function to the device driver. I really fail to see why hardware
manufacturers consider the reset sequence to be a state secret.
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