From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:51387) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tb2Of-00047Y-6H for qemu-devel@nongnu.org; Tue, 20 Nov 2012 23:58:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Tb2Od-0003Qt-W4 for qemu-devel@nongnu.org; Tue, 20 Nov 2012 23:58:49 -0500 Date: Wed, 21 Nov 2012 16:00:32 +1100 From: David Gibson Message-ID: <20121121050032.GS18362@truffula.fritz.box> References: <1352774820-22804-1-git-send-email-david@gibson.dropbear.id.au> <1352774820-22804-13-git-send-email-david@gibson.dropbear.id.au> <7D986011-0512-4492-92AE-F8A331C9FB4A@suse.de> <20121119225143.GD18362@truffula.fritz.box> <93E0DBC0-8611-4AF5-8035-B4AD409DD0D3@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <93E0DBC0-8611-4AF5-8035-B4AD409DD0D3@suse.de> Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH 12/12] pseries: Generate unique LIOBNs for PCI host bridges List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: "qemu-ppc@nongnu.org List" , qemu-devel qemu-devel , "Michael S. Tsirkin" On Tue, Nov 20, 2012 at 10:27:11AM +0100, Alexander Graf wrote: > > On 19.11.2012, at 23:51, David Gibson wrote: > > > On Mon, Nov 19, 2012 at 05:34:12PM +0100, Alexander Graf wrote: > >> > >> On 13.11.2012, at 03:47, David Gibson wrote: > >> > >>> From: Alexey Kardashevskiy > >>> > >>> In future (with VFIO) we will have multiple PCI host bridges on > >>> pseries. Each one needs a unique LIOBN (IOMMU id). At the moment we > >>> derive these from the pci domain number, but the whole notion of > >>> domain numbers on the qemu side is bogus and in any case they're not > >>> actually uniquely allocated at this point. > >>> > >>> This patch, therefore uses a simple sequence counter to generate > >>> unique LIOBNs for PCI host bridges. > >>> > >>> Signed-off-by: Alexey Kardashevskiy > >>> Signed-off-by: David Gibson > >> > >> I don't really like the idea of having a global variable just > >> because our domain ID generation seems to not work as > >> expected. Michael, any comments here? > > > > Well, the patch I sent which changed domain id generation was > > ignored. In any case, as I said, the whole concept of domain numbers > > Michael? > > > makes no sense on the qemu side, so I don't think increasing reliance > > on them by using them here is a good idea. > > > > It would be conceptually nicer to derive the liobn from the buid, but > > that would rely on the buid's being unique in the low 32-bits, which > > is true in practice, but seems risky to rely on. > > Well, there has to be some uniqueness from the guest's POV already, > no? Yes, the BUIDs are unique, but they are 64-bit, whereas the LIOBN is only 32-bit. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson