Re: [NILO-discuss] Zen and the art of running in real mode

[Michael B. <mb...@fe...>]

On Tue, 8 Mar 2005, Marty Connor wrote:
> > Not all drivers *can* be modified to use in/out (i.e. portio) as
> > opposed to read/write (i.e. MMIO.)  It's a function of the hardware.
> So does this mean that any loader being used with these cards would have
> to use PM to have any chance of working?

In practical terms, yes.

> > Perhaps the first thing to do is to print a legible message if
> > something tries to call the PM entry point and/or invoke the RM entry
> > point in V86 mode.  Something asking them to report what they're
> > trying to do, and we could evaluate the importance at that point.
> Is this what we think FreeBSD is doing when talking to Etherboot?

Yes.

To be fair: I haven't *tried* FreeBSD's PXE loader in bochs to see what it 
does, but I can see from the code that it uses V86 mode and people have 
reported that it does, indeed, fail.

> I get the feeling that success may depend on:
>      - Whether there card uses MMIO or portio
>      - Whether the loader they intend to use tries to:
>        "call the PM entry point and/or invoke the RM entry point in V86 
> mode"
> 
> Now, since most people probably don't know the answer to either of 
> these questions, I think we might have to recommend options based on 
> either scenarios, or most-likely-to-work options (e.g. "Try this first 
> unless you are planning to boot FREEBSD" or "If you are planning to use 
> RIS, check this box").

The MMIO/portio issue is driver-specific.  Drivers that use MMIO will use 
readX/writeX.  Since these functions won't work under -DKEEP_IT_REAL, we 
could just make the compiler throw an error.

Michael