From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:55440) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TbA5J-0006DF-8q for qemu-devel@nongnu.org; Wed, 21 Nov 2012 08:11:23 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TbA59-00061i-Ba for qemu-devel@nongnu.org; Wed, 21 Nov 2012 08:11:21 -0500 Date: Wed, 21 Nov 2012 15:13:39 +0200 From: "Michael S. Tsirkin" Message-ID: <20121121131339.GA5730@redhat.com> 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> <20121120122608.GA1756@redhat.com> <20121121005705.GM18362@truffula.fritz.box> <20121121113448.GA31911@redhat.com> <20121121123600.GV18362@truffula.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121121123600.GV18362@truffula.fritz.box> 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: David Gibson Cc: "qemu-ppc@nongnu.org List" , qemu-devel qemu-devel On Wed, Nov 21, 2012 at 11:36:00PM +1100, David Gibson wrote: > On Wed, Nov 21, 2012 at 01:34:48PM +0200, Michael S. Tsirkin wrote: > > On Wed, Nov 21, 2012 at 11:57:05AM +1100, David Gibson wrote: > > > On Tue, Nov 20, 2012 at 02:26:09PM +0200, Michael S. Tsirkin wrote: > > > > 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? > > > > > > > > This is user visible, right? > > > > So IMHO we should have the user specify LIOBN through a property, > > > > rather than assign what's essentially a random value. > > > > > > Well, I can implement an override through a property, which could be > > > useful in some circumstances. But we still need to have qemu generate > > > unique defaults, rather than forcing it to be specified in every case. > > > > I don't see why. > > And if you want automatic defaults then they need to be generated in a > > way that does not depend on implementation detail such as order of > > device initialization. > > Because requiring explicit unique liobns to be supplied whenever there > is more than one PHB is horrible for usability. We should make simple things simple and complex things possible. More than one PHB seems like an advanced feature so I don't see why it needs to be made very easy to use. With an appropriate error message it should not be too hard for users to figure it out. > -- > 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