Re: clean way to support >32bit addr on 32bit CPU

Linus Torvalds
2005-01-11T01:31:12Z

On Mon, 10 Jan 2005, Randy.Dunlap wrote:
>
> Speaking of fall-out, or more like trickle-down,
> I'm almost done with a patch to make PCMCIA resources use
> unsigned long instead of u_int or u_short for IO address:

Ahh, yes. That's required on pretty much all platforms except x86 and
x86-64.

Of course, since ARM and MIPS already do the "u_int" thing, and not a
whole lot of other architectures do PCMCIA, I guess it doesn't matter
_that_ much. Cardbus stuff should get it right regardless.

> typedef unsigned long ioaddr_t;
>
> and then include/pcmcia/cs.c needs some changes in use of
> ioaddr_t, along with drivers (printk formats).
>
> Does that sound OK?
> I guess that it would become unsigned long long (or u64)
> with this proposal?

I don't think ioaddr_t needs to match resources. None of the IO accessor
functions take "u64"s anyway - and aren't likely to do so in the future
either - so "unsigned long" should be good enough.

Having u64 for resource handling is mainly an issue for RAM and
memory-mapped IO (right now the 32-bit limit means that we throw away
information about stuff above the 4GB mark from the e820 interfaces on
x86, for example - that _happens_ to work because we never see anything
but RAM there anyway, but it means that /proc/iomem doesn't show all of
the system RAM, and it does mean that our resource management doesn't
actually handle 64-bit addresses correctly.

See drivers/pci/probe.c for the result:

"PCI: Unable to handle 64-bit address for device xxxx"

(and I do not actually think this has _ever_ happened in real life, which
makes me suspect that Windows doesn't handle them either - but it
inevitably will happen some day).

Linus