From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:57710) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TbAKp-0003Yh-JP for qemu-devel@nongnu.org; Wed, 21 Nov 2012 08:27:29 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TbAKf-0002Ah-UE for qemu-devel@nongnu.org; Wed, 21 Nov 2012 08:27:23 -0500 Message-ID: <50ACD6AC.6030001@suse.de> Date: Wed, 21 Nov 2012 14:27:08 +0100 From: Alexander Graf MIME-Version: 1.0 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> <20121121131339.GA5730@redhat.com> <20121121132157.GW18362@truffula.fritz.box> In-Reply-To: <20121121132157.GW18362@truffula.fritz.box> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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 , "Michael S. Tsirkin" On 11/21/2012 02:21 PM, David Gibson wrote: > On Wed, Nov 21, 2012 at 03:13:39PM +0200, Michael S. Tsirkin wrote: >> 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 > Not for pseries. On real hardware of this type, dozens of PHBs is > routine. Plus, vfio passthrough is coming, we need at minimum one PHB > for emulated devices and one for passthrough devices. Yeah, I second Davids opinion here. We need to make this easy for users. How do we assign PCI slot IDs today when all you do is a -device? This should probably follow the same scheme. Alex