From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: Re: [PATCH v2 1/2] PCI: Add PCI device flag PCI_DEV_FLAGS_DMA_ALIAS_ROOT Date: Thu, 23 Jun 2016 13:04:01 +0100 Message-ID: <576BD031.7090105@arm.com> References: <1462700001-30086-1-git-send-email-jchandra@broadcom.com> <5730621B.2050503@arm.com> <573340F9.6050507@arm.com> <037404e2-3168-8f99-0bdb-bb929776108e@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <037404e2-3168-8f99-0bdb-bb929776108e-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Jon Masters , Jayachandran C Cc: linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Bjorn Helgaas , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: iommu@lists.linux-foundation.org On 23/06/16 06:01, Jon Masters wrote: > On 05/11/2016 10:26 AM, Robin Murphy wrote: >> (I have no actual objection to this patch, though, and at this point >> I'm just chucking ideas about). > > Can I ask what the next steps are here? We're looking for upstream > direction to guide some internal activities and could really do with > understanding how you'd like to solve this one longer term as well as > what interim solution could be acceptable until we get there. Well, for now I'm planning to leave the explicit "terminate the alias walk from the callback function" behaviour in the DT-parsing code[1], since there doesn't seem any good reason not to. As Bjorn says, though, it probably is generally useful for the PCI code to have its own knowledge of exactly where DMA can escape the PCI hierarchy - I now wonder if we could actually just do that from the DT/IORT code; if firmware says a particular bridge/etc. has a relationship with an ITS or SMMU, then presumably it's reasonable to infer that DMA can come out of it, thus we could inform the PCI code there and then without it having to quirk things on its own? Robin. [1]:http://article.gmane.org/gmane.linux.kernel.iommu/13932 > > Jon. > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Subject: Re: [PATCH v2 1/2] PCI: Add PCI device flag PCI_DEV_FLAGS_DMA_ALIAS_ROOT To: Jon Masters , Jayachandran C References: <1462700001-30086-1-git-send-email-jchandra@broadcom.com> <5730621B.2050503@arm.com> <573340F9.6050507@arm.com> <037404e2-3168-8f99-0bdb-bb929776108e@redhat.com> Cc: Alex Williamson , iommu@lists.linux-foundation.org, Bjorn Helgaas , linux-pci@vger.kernel.org From: Robin Murphy Message-ID: <576BD031.7090105@arm.com> Date: Thu, 23 Jun 2016 13:04:01 +0100 MIME-Version: 1.0 In-Reply-To: <037404e2-3168-8f99-0bdb-bb929776108e@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed List-ID: On 23/06/16 06:01, Jon Masters wrote: > On 05/11/2016 10:26 AM, Robin Murphy wrote: >> (I have no actual objection to this patch, though, and at this point >> I'm just chucking ideas about). > > Can I ask what the next steps are here? We're looking for upstream > direction to guide some internal activities and could really do with > understanding how you'd like to solve this one longer term as well as > what interim solution could be acceptable until we get there. Well, for now I'm planning to leave the explicit "terminate the alias walk from the callback function" behaviour in the DT-parsing code[1], since there doesn't seem any good reason not to. As Bjorn says, though, it probably is generally useful for the PCI code to have its own knowledge of exactly where DMA can escape the PCI hierarchy - I now wonder if we could actually just do that from the DT/IORT code; if firmware says a particular bridge/etc. has a relationship with an ITS or SMMU, then presumably it's reasonable to infer that DMA can come out of it, thus we could inform the PCI code there and then without it having to quirk things on its own? Robin. [1]:http://article.gmane.org/gmane.linux.kernel.iommu/13932 > > Jon. >