From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH 3/3] virtio PCI device Date: Tue, 27 Nov 2007 10:25:59 +0100 Message-ID: <200711271026.00084.arnd@arndb.de> References: <11944899922822-git-send-email-aliguori@us.ibm.com> <474B1BF3.20901@us.ibm.com> <474BDD28.7050801@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <474BDD28.7050801-atKUWr5tajBWk0Htik3J/w@public.gmane.org> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Cc: Eric Van Hensbergen , kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, lguest , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, virtualization-qjLDD68F18O7TbgM5vRIOg@public.gmane.org List-Id: virtualization@lists.linuxfoundation.org On Tuesday 27 November 2007, Avi Kivity wrote: > > :-) =A0Do you know if there is a hard limit on the number of devices on = > > a PCI bus? =A0My concern was that it was limited by something stupid = > > like an 8-bit identifier. > = > IIRC pci slots are 8-bit, but you can have multiple buses, so = > effectively 16 bits of device address space (discounting functions which = > are likely not hot-pluggable). You have an 8 bit bus number and an 8 bit device/function number. The function number is 3 bits, so if you want to use only function 0 for everything, you are limited to a little under 8192 (2^(8+5)) devices per PCI domain. PC style hardware cannot easily address multiple PCI domains, but I think you can have them if you assume that the guest is using mmconfig. For using multiple buses, the easiest way could be to have every device/function on bus 0 be a bridge by itself, so you end up with a flat number space for the actual devices, $ lspci -t [0000:00]-+-00.0-[0000:01]--+-00.0 | +-01.0 | +-02.0 | + ... | \-3f.0 +-00.1-[0000:02]--+-00.0 | +-01.0 | +-02.0 | + ... | \-3f.0 + ... | +-3f.6-[0000:ff]--+-00.0 +-01.0 +-02.0 + ... \-3f.0 Arnd <>< ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/