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SubjectRe: proper ioport space allocation
On Thu, Dec 17, 1998 at 10:22:18AM -0600, Bob McElrath wrote:
> I've been playing with the pas2 (sound) module on my Alpha (because it works
> on Intel, but not Alpha), and have discovered that this module never
> allocates any portspace. (i.e. cat /proc/ioports shows no mention of the
> PAS16 driver). Now in looking through the developer's kit and such I have
> discovered that this card uses an absolute boatload of portspace. It starts
> at 0x388 and uses harmonics (of 0x400) above that, as well as one other
> random port. (List below)

2^10 = 0x400.
Old ISA cards only used 10bits for decoding the address, so they felt
addressed even when their address + 0x400 ... was used. I will call this
ISA aliasing for now.
I think your PAS card knows how to decode all 16 bits of the ISA bus. Just
the driver checks, that there are no other cards having allocated aliases of
the requested address, assuming the other card might be stupid enough to
only decode 10bits.
It should be fine to check for the aliases and printk a warning, or abort
with an error message, if the PAS only uses 10bits. Does anybody know this?

In any case, I would only register one address and not all the aliases.

--
Kurt Garloff <K.Garloff@ping.de> (Dortmund, FRG)
PGP key on http://student.physik.uni-dortmund.de/homepages/garloff

There is something frustrating about the quality and speed of Linux
development. I.e. the quality is too high and the speed is too high, in
other words, I can implement this XXXX feature, but I bet someone else
has already done it and is just about to release his patch to Linus soon...
[From a posting of Tigran Aivazian to linux-kernel, XXXX = disk stat]

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