From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0846DC3F2C6 for ; Tue, 3 Mar 2020 13:02:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D9D7A2086A for ; Tue, 3 Mar 2020 13:02:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728434AbgCCNCB (ORCPT ); Tue, 3 Mar 2020 08:02:01 -0500 Received: from 8bytes.org ([81.169.241.247]:49780 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728361AbgCCNCB (ORCPT ); Tue, 3 Mar 2020 08:02:01 -0500 Received: by theia.8bytes.org (Postfix, from userid 1000) id E1C66385; Tue, 3 Mar 2020 14:01:59 +0100 (CET) Date: Tue, 3 Mar 2020 14:01:56 +0100 From: Joerg Roedel 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 Subject: Re: [PATCH v2 1/3] iommu/virtio: Add topology description to virtio-iommu config space 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 Content-Disposition: inline In-Reply-To: <9004f814-2f7c-9024-3465-6f9661b97b7a@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.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