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Thu, 16 Sep 2021 08:26:41 +0100 From: Shameerali Kolothum Thodi To: Jon Nettleton , Robin Murphy Subject: RE: [PATCH v7 2/9] ACPI/IORT: Add support for RMR node parsing Thread-Topic: [PATCH v7 2/9] ACPI/IORT: Add support for RMR node parsing Thread-Index: AQHXidEiKr58723PTUGGkSglF1QKPatlAmqAgDJmwoCAACN+gIAO55og Date: Thu, 16 Sep 2021 07:26:41 +0000 Message-ID: References: <20210805080724.480-1-shameerali.kolothum.thodi@huawei.com> <20210805080724.480-3-shameerali.kolothum.thodi@huawei.com> <20210805160319.GB23085@lpieralisi> <5d9bebdf-6eb5-49a0-2e8f-490df2d6754d@arm.com> In-Reply-To: Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.47.83.177] MIME-Version: 1.0 X-CFilter-Loop: Reflected Cc: Steven Price , ACPI Devel Maling List , Linux IOMMU , wanghuiqiang , "Guohanjun \(Hanjun Guo\)" , yangyicong , Sami Mujawar , Will Deacon , linux-arm-kernel X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" > -----Original Message----- > From: Jon Nettleton [mailto:jon@solid-run.com] > Sent: 06 September 2021 20:51 > To: Robin Murphy > Cc: Lorenzo Pieralisi ; Shameerali Kolothum Thodi > ; Laurentiu Tudor > ; linux-arm-kernel > ; ACPI Devel Maling List > ; Linux IOMMU > ; Linuxarm ; > Joerg Roedel ; Will Deacon ; > wanghuiqiang ; Guohanjun (Hanjun Guo) > ; Steven Price ; Sami > Mujawar ; Eric Auger ; > yangyicong > Subject: Re: [PATCH v7 2/9] ACPI/IORT: Add support for RMR node parsing > [...] > > > > > > On the prot value assignment based on the remapping flag, I'd like > > > to hear Robin/Joerg's opinion, I'd avoid being in a situation where > > > "normally" this would work but then we have to quirk it. > > > > > > Is this a valid assumption _always_ ? > > > > No. Certainly applying IOMMU_CACHE without reference to the device's > > _CCA attribute or how CPUs may be accessing a shared buffer could lead > > to a loss of coherency. At worst, applying IOMMU_MMIO to a > > device-private buffer *could* cause the device to lose coherency with > > itself if the memory underlying the RMR may have allocated into system > > caches. Note that the expected use for non-remappable RMRs is the > > device holding some sort of long-lived private data in system RAM - > > the MSI doorbell trick is far more of a niche hack really. > > > > At the very least I think we need to refer to the device's memory > > access properties here. > > > > Jon, Laurentiu - how do RMRs correspond to the EFI memory map on your > > firmware? I'm starting to think that as long as the underlying memory > > is described appropriately there then we should be able to infer > > correct attributes from the EFI memory type and flags. > > The devices are all cache coherent and marked as _CCA, 1. The Memory > regions are in the virt table as ARM_MEMORY_REGION_ATTRIBUTE_DEVICE. > > The current chicken and egg problem we have is that during the fsl-mc-bus > initialization we call > > error = acpi_dma_configure_id(&pdev->dev, DEV_DMA_COHERENT, > &mc_stream_id); > > which gets deferred because the SMMU has not been initialized yet. Then we > initialize the RMR tables but there is no device reference there to be able to > query device properties, only the stream id. After the IORT tables are parsed > and the SMMU is setup, on the second device probe we associate everything > based on the stream id and the fsl-mc-bus device is able to claim its 1-1 DMA > mappings. Can we solve this order problem by delaying the iommu_alloc_resv_region() to the iommu_dma_get_rmr_resv_regions(dev, list) ? We could invoke device_get_dma_attr() from there which I believe will return the _CCA attribute. Or is that still early to invoke that? Thanks, Shameer > cat /sys/kernel/iommu_groups/0/reserved_regions > 0x0000000001000000 0x0000000010ffffff direct-relaxable > 0x0000000008000000 0x00000000080fffff msi > 0x000000080c000000 0x000000081bffffff direct-relaxable > 0x0000001c00000000 0x0000001c001fffff direct-relaxable > 0x0000002080000000 0x000000209fffffff direct-relaxable > > -Jon > > > > > Robin. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu