From: "Michael S. Tsirkin" <mst@redhat.com> To: Jean-Philippe Brucker <jean-philippe.brucker@arm.com> Cc: "virtio-dev@lists.oasis-open.org" <virtio-dev@lists.oasis-open.org>, "kevin.tian@intel.com" <kevin.tian@intel.com>, Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>, "tnowicki@caviumnetworks.com" <tnowicki@caviumnetworks.com>, "frowand.list@gmail.com" <frowand.list@gmail.com>, "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>, "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>, "joro@8bytes.org" <joro@8bytes.org>, "virtualization@lists.linux-foundation.org" <virtualization@lists.linux-foundation.org>, "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>, "robh+dt@kernel.org" <robh+dt@kernel.org>, "kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>, "bhelgaas@google.com" <bhelgaas@google.com>, Robin Murphy <Robin.Murphy@arm.com>, "jasowang@redhat.com" <jasowang@redhat.com>, "bauerman@linux.ibm.com" <bauerman@linux.ibm.com> Subject: Re: [virtio-dev] Re: [PATCH v8 2/7] dt-bindings: virtio: Add virtio-pci-iommu node Date: Sun, 16 Jun 2019 16:04:49 -0400 Message-ID: <20190616154841-mutt-send-email-mst@kernel.org> (raw) In-Reply-To: <c3cd5dba-123d-e808-98b1-731ac2d4b950@arm.com> On Fri, May 31, 2019 at 12:13:47PM +0100, Jean-Philippe Brucker wrote: > On 30/05/2019 18:45, Michael S. Tsirkin wrote: > > On Thu, May 30, 2019 at 06:09:24PM +0100, Jean-Philippe Brucker wrote: > >> Some systems implement virtio-iommu as a PCI endpoint. The operating > >> system needs to discover the relationship between IOMMU and masters long > >> before the PCI endpoint gets probed. Add a PCI child node to describe the > >> virtio-iommu device. > >> > >> The virtio-pci-iommu is conceptually split between a PCI programming > >> interface and a translation component on the parent bus. The latter > >> doesn't have a node in the device tree. The virtio-pci-iommu node > >> describes both, by linking the PCI endpoint to "iommus" property of DMA > >> master nodes and to "iommu-map" properties of bus nodes. > >> > >> Reviewed-by: Rob Herring <robh@kernel.org> > >> Reviewed-by: Eric Auger <eric.auger@redhat.com> > >> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com> > > > > So this is just an example right? > > We are not defining any new properties or anything like that. > > Yes it's just an example. The properties already exist but it's good to > describe how to put them together for this particular case, because > there isn't a precedent describing the topology for an IOMMU that > appears on the PCI bus. > > > I think down the road for non dt platforms we want to put this > > info in the config space of the device. I do not think ACPI > > is the best option for this since not all systems have it. > > But that can wait. > > There is the probe order problem - PCI needs this info before starting > to probe devices on the bus. This isn't all that special - it's pretty common for IOMMUs to be pci devices. The solution is to have the device on bus 0. For example, add it with DECLARE_PCI_FIXUP_EARLY or DECLARE_PCI_FIXUP_CLASS_EARLY in e.g. arch/x86/kernel/quirks.c or drivers/pci/quirks.c You can also use the configuration access capability if there's need to access the device before its memory is enabled. > Maybe we could store the info in a separate > memory region, that is referenced on the command-line and that the guest > can read early. > > Thanks, > Jean The point is to avoid command line hacks. Devices should be self describing. -- MST _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
next prev parent reply index Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-05-30 17:09 [PATCH v8 0/7] Add virtio-iommu driver Jean-Philippe Brucker 2019-05-30 17:09 ` [PATCH v8 1/7] dt-bindings: virtio-mmio: Add IOMMU description Jean-Philippe Brucker 2019-05-30 17:09 ` [PATCH v8 2/7] dt-bindings: virtio: Add virtio-pci-iommu node Jean-Philippe Brucker 2019-05-30 17:45 ` Michael S. Tsirkin 2019-05-31 11:13 ` [virtio-dev] " Jean-Philippe Brucker 2019-06-16 20:04 ` Michael S. Tsirkin [this message] 2019-05-30 17:09 ` [PATCH v8 3/7] of: Allow the iommu-map property to omit untranslated devices Jean-Philippe Brucker 2019-05-30 17:09 ` [PATCH v8 4/7] PCI: OF: Initialize dev->fwnode appropriately Jean-Philippe Brucker 2019-05-30 17:09 ` [PATCH v8 5/7] iommu: Add virtio-iommu driver Jean-Philippe Brucker 2019-06-14 7:33 ` Auger Eric 2019-05-30 17:09 ` [PATCH v8 6/7] iommu/virtio: Add probe request Jean-Philippe Brucker 2019-05-30 17:09 ` [PATCH v8 7/7] iommu/virtio: Add event queue Jean-Philippe Brucker 2019-06-13 15:54 ` [PATCH v8 0/7] Add virtio-iommu driver Auger Eric
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