Date: Wed, 24 Nov 2004 08:22:20 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: cswiger@mac.com Cc: freebsd-current@freebsd.org Subject: Re: Transparent bridges (a. k. a. HUB-to-PCI bridges)? Message-ID: <20041124.082220.29053157.imp@bsdimp.com> In-Reply-To: <41A49A7B.6020009@mac.com> References: <41A416E7.4030107@mac.com> <20041123.235250.118899687.imp@bsdimp.com> <41A49A7B.6020009@mac.com>
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In message: <41A49A7B.6020009@mac.com>
Chuck Swiger <cswiger@mac.com> writes:
: M. Warner Losh wrote:
: > In message: <41A416E7.4030107@mac.com>
: > Chuck Swiger <cswiger@mac.com> writes:
: [ ... ]
: > : A host-PCI bridge is typically part of the "southbridge" chip of modern
: > : motherboards; on Intel motherboards this is also called the ICH chip, such as
: > : the 82801AA/BA/CA/etc. VIA Southbridges include the VT8233/8235/8237/etc.
: > :
: > : A PCI-PCI bridge is commonly found on multifunction PCI cards, an example
: > : would be the DEC 21151 chip found on various four-port NICs.
: >
: > Newer laptops (and other machines) typically have a PCI PCI bridge
: > that all the builtin hardware lives behind. Many, but not all, of
: > these bridges are transparent pci pci bridges, maning they act much
: > like a subtractively decoded bridge.
:
: You are absolutely right; the impression I got was that laptops like to have
: PCI-PCI bridges in order to make it easier to route interrupts for devices on
: a docking station or the like. If they don't use such a PCI-PCI bridge chip,
: then the laptop's BIOS needs to set up a $PIR table which routes interrupts
: properly for _all_ of the possible docking station configurations and devices
: to which the laptop might be attached to.
:
: Making things work right with a known configuration seems to be hard enough
: for some vendors, so it's not surprising that pre-planning for possible future
: configurations is difficult to do without using a PCI-PCI bridge to aggregate
: the devices lurking behind it.
Having a pci-pci bridge is no guarantee that the interrupts will be
routed correctly. Many laptops route them directly, even in the face
of a pci-pci bridge. The $PIR will often lists devices behind the
bridge.
Warner
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