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Date:      Wed, 06 May 1998 00:44:49 -0700
From:      Mike Smith <mike@smith.net.au>
To:        Don Lewis <Don.Lewis@tsc.tdk.com>
Cc:        Mike Smith <mike@smith.net.au>, Archie Cobbs <archie@whistle.com>, stefan@promo.de (Stefan Bethke), luigi@labinfo.iet.unipi.it, freebsd-hackers@FreeBSD.ORG
Subject:   Re: ISA-PnP w\o BIOS support? 
Message-ID:  <199805060744.AAA01906@antipodes.cdrom.com>
In-Reply-To: Your message of "Wed, 06 May 1998 01:20:04 PDT." <199805060820.BAA20482@salsa.gv.tsc.tdk.com> 

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> On May 5, 11:26pm, Mike Smith wrote:
> } Subject: Re: ISA-PnP w\o BIOS support?
> 
> } This actually falls a little short.  It's easier to look at it from a 
> } different angle, too.
> } 
> }   For each PnP device/function in the system
> }     If the device/function is not supported (unknown, no driver present)
> }       deconfigure device (if required)
> }       continue
> }     else
> }       while resources required
> }         allocate new resources
> }         test resources (using PnP test facility if available)
> }       endwhile
> }       if resources available
> }         allocate a new driver instance, assign resources
> }       else
> }         continue
> }     endif
> }   endfor
> } 
> }   For each explicitly-configured ISA devices
> }     if resource config does not conflict with PnP-configured device
> }       allocate resources
> }       if probe succeeds
> }         allocate new driver instance
> }       else
> }         free resources
> }       endif
> }     endif
> }   endfor
> 
> Why would you not want to reverse the order and configure the explicitly
> configured ISA devices first and the PnP devices last?

Because your brute-force probe may find a device that is actually a PnP 
device, and which has been allocated resources by the BIOS.

> If you configure
> the PnP devices first, they might use resources required by the ISA
> devices.

In most cases, this is not possible.  You can detect I/O and memory 
conflicts using the probe techniques, and IRQ conflicts are impossible 
on systems that support BIOS configuration of resources.

> If you configure the ISA devices first, then you should be
> able to adjust the resources used by the PnP devices so they don't
> conflict with the ISA devices.

Given that resource conflicts are pretty unlikely, this isn't a real 
problem.  The actual relative ordering is not terribly important - on 
the plus side doing the ISA probe first lets you "wire down" specific 
devices to IO combinations, but it loses insofar as you may get a less 
than optimal driver/device match just because the device matched an ISA 
probe instead.

-- 
\\  Sometimes you're ahead,       \\  Mike Smith
\\  sometimes you're behind.      \\  mike@smith.net.au
\\  The race is long, and in the  \\  msmith@freebsd.org
\\  end it's only with yourself.  \\  msmith@cdrom.com



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