Re: proper ioport space allocation

Kurt Garloff (garloff@kg1.ping.de)
Thu, 17 Dec 1998 22:36:59 +0100

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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