Re: IO delay, port 0x80, and BIOS POST codes

[ebiederm@xmission.com (Eric W. Biederman)]

Linus Torvalds <torvalds@transmeta.com> writes:

> On Thu, 14 Mar 2002, John Heil wrote:
> > 
> > No, the better/correct port is 0xED which removes the conflict.
> 
> Port ED is fine for a BIOS, which (by definition) knows what the
> motherboard devices are, and thus knows that ED cannot be used by
> anything.
> 
> But it _is_ an unused port, and that's exactly the kind of thing that
> might be used sometime in the future. Remember the port 22/23 brouhaha
> with Cyrix using it for their stuff, and later Intel getting into the fray
> too?
> 
> So the fact that ED works doesn't mean that _stays_ working.
> 
> The fact that 80 is the post code register means that it is fairly likely 
> to _stay_ that way, without any ugly surprises.
> 
> Now, if there is something _else_ than just the fact that it is unused
> that makes ED a good choice in the future too, that might be worth looking
> into (like NT using it for the same purpose as Linux does port 80),

Does the logic outb_p uses continue to work if you have a PCI post
card (possibly on the motherboard).  And an ISA device?

Systems without ISA slots but with ISA or LPC devices onboard must
use a PCI post card so I have trouble believing that outb_b and friends
really work as expected....


Eric