Re: PC System BIOS and Base Address Register

[v_chau@emulex.com (Vi Chau)]

> 
> I understand this is just a detail, and it is a good thing that
> BIOSes scan all BARs. However, we should talk about DEVICE compliance
> and not BIOS compliance.
> 
> A spec is a spec and the PCI spec says (as reported also by Bob
> Goudreau):
> 	
> 	"The first Base Address register is always located at offset
> 	10h.  The second register may be at offset 14h or 18h
> 	depending on the size of the first.  The offsets of 
> 	subsequent Base Address registers are determined by the 
> 	size of previous Base Address registers."
> 
> So, w_wong@emulex.com's implementation, whether acceptable, is
> unfortunately not respecting the PCI spec (since he is not using 
> 64 bits addressing, he must use 14h for his second BAR). Unless
> somebody can prove that "may be" is to be interpreted as
> "if you want it can be"...
> 
> What is the impact of this divergence from the spec? None, thanks
> to those who wrote the BIOS compliance tests. But maybe future revisions
> of the spec should have one more line to clear up this issue more
> precisely.
> 
> Thanks for your attention,
> 
> 				
> 				Daniele


The implementation in question supports 64-bit addressing so that two BAR's
are used for one address region. However, we can change the lower 4 bits of
the BAR so that the region can be re-defined as memory or I/O and in case of
memory, its type can be changed. When we request to be mapped below 1MB,
the high-order BAR is unused and that's the root of the question. We can
make the high-order BAR read-only but we do not want to map it out so that it
disappear from the config space.

If the BIOS's scan all of the BAR area then it seems that we will be ok when
requesting to be mapped below 1MB.

I can see emails coming to tell me that requesting to be mapped below 1MB is
"discourage" but that's another problem; please see our other question about
DOS, protected mode and all that good stuff.


Vi Chau
Emulex Corp.
3535 Harbor Blvd.
Costa Mesa, CA 92626
ù˜†