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Tue, 27 Oct 2026 03:42:36 +0000 Received: from SJ2PR12MB9161.namprd12.prod.outlook.com ([fe80::d9d1:8c49:a703:b017]) by SJ2PR12MB9161.namprd12.prod.outlook.com ([fe80::d9d1:8c49:a703:b017%5]) with mapi id 15.21.0546.021; Tue, 27 Oct 2026 03:42:36 +0000 From: Mikko Perttunen To: Alistair Popple , linux-rdma@vger.kernel.org Cc: dri-devel@lists.freedesktop.org, christian.koenig@amd.com, sumit.semwal@linaro.org, jgg@nvidia.com, Thomas =?UTF-8?B?SGVsbHN0csO2bQ==?= , Simona Vetter , Matthew Brost , Vivek Kasireddy , Dongwon Kim , Leon Romanovsky , Kevin Tian , Xu Yilun , Baolu Lu , Felix Kuehling , Alex Deucher , intel-xe@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-rdma@vger.kernel.org, iommu@lists.linux.dev, Alexey Kardashevskiy , zhipingz@meta.com, treding@nvidia.com, jhubbard@nvidia.com, Karl Mehltretter Subject: Re: [PATCH 23/26] treewide: Rename dma_buf_attach() to dma_buf_sgt_attach() Date: Tue, 27 Oct 2026 12:42:32 +0900 Message-ID: In-Reply-To: References: <20261026053623.202642-1-apopple@nvidia.com> <20261026053623.202642-24-apopple@nvidia.com> Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; 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A 3 MiB system-hea= p > buffer was imported into Tegra DRM and scanned out over HDMI. With > CONFIG_DMABUF_DEBUG=3Dy the PRIME import succeeded, but scanout immediate= ly > produced display SMMU faults starting at 0x300000. >=20 > Tracing the fault led here: >=20 > > @@ -475,7 +475,7 @@ static struct tegra_bo *tegra_bo_import(struct drm_= device *drm, > > * domain, map it first to the DRM device to get an sgt. > > */ > > if (tegra->domain) { > > - attach =3D dma_buf_attach(buf, drm->dev); > > + attach =3D dma_buf_sgt_attach(buf, drm->dev); >=20 > tegra_bo_import() passes the attachment SGT to iommu_map_sgtable(), which > uses sg_phys() and sg->length. The SGT mapping contract only guarantees t= he > DMA address and length fields. The debug wrapper clears the page-side fie= lds, > so iommu_map_sgtable() maps zero bytes.=20 >=20 > Tegra only treats negative returns as errors and keeps the reserved > IOVA, which scanout then faults on. >=20 > This page-side use predates the series, so the fault is not itself a v2 > regression. Is dma_buf_sgt_attach() valid for this call site, or does Teg= ra > need a page/physical mapping type first? >=20 > Karl >=20 Sounds like a bug in TegraDRM; we should be using the DMA addr/length=20 for the explicit IOMMU mapping as the sgt attachment is for the dummy=20 DRM device explicitly intended to give us physical addresses. I'm currently in the process of removing the whole explicit IOMMU path=20 so if this only occurs with CONFIG_DMABUF_DEBUG enabled, I don't think=20 there's a pressing need to fix this before then. Thanks for the bug report! Mikko