Date: Wed, 24 Nov 2004 09:28:11 -0500 From: Chuck Swiger <cswiger@mac.com> To: "M. Warner Losh" <imp@bsdimp.com> Cc: freebsd-current@freebsd.org Subject: Re: Transparent bridges (a. k. a. HUB-to-PCI bridges)? Message-ID: <41A49A7B.6020009@mac.com> In-Reply-To: <20041123.235250.118899687.imp@bsdimp.com> References: <200411231343.22760.jhb@FreeBSD.org> <20041124002603.GD20881@squash.dsto.defence.gov.au> <41A416E7.4030107@mac.com> <20041123.235250.118899687.imp@bsdimp.com>
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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. -- -Chuck
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