On 15 Oct 2000, Chris G. Demetriou wrote:

> I disagree with the notion of a directory for every single chip of the
> PC super-io variety, or even this one unless there's some overriding
> reason -- i'm coming into this thread late, and this was the first
> message I saw about it.
> 
> If it's a PC super-io chip, what's wrong with just attaching an 'ISA'
> to it?

Its a possibility, though there are a few things I don't like about the
prospect:

 - At the moment, the upc driver reads the chip's configuration registers,
   and uses the results to locate the child devices.  Is this sensibly
   possible with an isa attachment?  If not, we have to fall back to
   probing for each device, which is grotty.
 - The UPC has the ability to power sections of the chip up and down,
   which should be used to eg turn off the serial ports when they're not
   in use.  While there's no code to handle this at present, I can imagine
   that it would get even harder to add with an isa interface in the way.
 - Devices attached at isa are expected to call bus_space_map themselves,
   which means the relevant bus_space_tag_t has to contain enough
   information to locate the UPC in the system's I/O space.  This is
   probably only a problem if you use a very simple bus_space
   implementation, though.

> that's what some ports do, unless i'm mistaken.

Which ones?  I'd like to see how it works in practice.

-- 
Ben Harris                                                   <bjh21@netbsd.org>
Portmaster, NetBSD/arm26               <URL:http://www.netbsd.org/Ports/arm26/>