Re: New kernel/resource.c

Alan Modra (alan@SPRI.Levels.UniSA.Edu.Au)
Mon, 26 Jul 1999 09:49:34 +0930 (CST)

On Sun, 25 Jul 1999, Linus Torvalds wrote:
>
> On Sun, 25 Jul 1999, Richard Henderson wrote:
> >
> > Hmm, actually we have more than 65536 generically on PCI. It's
> > just the x86 that limits to 64k. I actually ran into trouble
> > here the other day --
>
> Yeehaa..
>
> I wonder how many devices decode all 32 bits of an IO address. Maybe they
> all do, but it sure hasn't gotten any testing by anybody. Considering that

They aren't PCI compliant if they don't decode all 32 bits. Extract from
PCI v2.1 spec:

"The I/O Read command is used to read data from an agent mapped in I/O
Address Space. AD[31::00] provide a byte address. All 32 bits must be
decoded."

Ditto for I/O write. The area where PCI devices are likely to cheat on
address decoding is in the IO/mem base address regs, where some bits may
be hardwired to zeros.

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