From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH v2 1/3] iommu/virtio: Add topology description to virtio-iommu config space Date: Tue, 3 Mar 2020 14:01:56 +0100 Message-ID: <20200303130155.GA13185@8bytes.org> References: <20200228172537.377327-1-jean-philippe@linaro.org> <20200228172537.377327-2-jean-philippe@linaro.org> <20200302161611.GD7829@8bytes.org> <9004f814-2f7c-9024-3465-6f9661b97b7a@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <9004f814-2f7c-9024-3465-6f9661b97b7a@redhat.com> Sender: linux-pci-owner@vger.kernel.org To: Auger Eric Cc: Jean-Philippe Brucker , iommu@lists.linux-foundation.org, virtualization@lists.linux-foundation.org, linux-pci@vger.kernel.org, bhelgaas@google.com, mst@redhat.com, jasowang@redhat.com, kevin.tian@intel.com, sebastien.boeuf@intel.com, jacob.jun.pan@intel.com, robin.murphy@arm.com List-Id: virtualization@lists.linuxfoundation.org Hi Eric, On Tue, Mar 03, 2020 at 11:19:20AM +0100, Auger Eric wrote: > Michael has pushed this solution (putting the "configuration in the PCI > config space"), I think for those main reasons: > - ACPI may not be supported on some archs/hyps But on those there is device-tree, right? > - the virtio-iommu is a PCIe device so binding should not need ACPI > description The other x86 IOMMUs are PCI devices too and they definitly need a ACPI table to be configured. > Another issue with ACPI integration is we have different flavours of > tables that exist: IORT, DMAR, IVRS An integration with IORT might be the best, but if it is not possible ther can be a new table-type for Virtio-iommu. That would still follow platform best practices. > x86 ACPI integration was suggested with IORT. But it seems ARM is > reluctant to extend IORT to support para-virtualized IOMMU. So the VIOT > was proposed as a different atternative in "[RFC 00/13] virtio-iommu on > non-devicetree platforms" > (https://patchwork.kernel.org/cover/11257727/). Proposing a table that > may be used by different vendors seems to be a challenging issue here. Yeah, if I am reading that right this proposes a one-fits-all solution. That is not needed as the other x86 IOMMUs already have their tables defined and implemented. There is no need to change anything there. > So even if the above solution does not look perfect, it looked a > sensible compromise given the above arguments. Please could you explain > what are the most compelling arguments against it? It is a hack and should be avoided if at all possible. And defining an own ACPI table type seems very much possible. Regards, Joerg