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[2a02:3100:b305:2001:39fa:3d24:821a:4eae]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a027741586sm315273615e9.14.2026.10.04.23.46.44 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 04 Oct 2026 23:46:45 -0700 (PDT) From: Karl Mehltretter To: Sumit Semwal , =?UTF-8?q?Christian=20K=C3=B6nig?= Cc: Karl Mehltretter , Benjamin Gaignard , Brian Starkey , John Stultz , "T . J . Mercier" , Jason Gunthorpe , Dmitry Osipenko , Mauro Carvalho Chehab , Thierry Reding , Jonathan Hunter , Russell King , David Airlie , Simona Vetter , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 0/3] dma-buf: heaps: cma: respect the importer's maximum segment size Date: Mon, 5 Oct 2026 08:46:37 +0200 Message-Id: <20261005064640.7776-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The CMA heap builds attachment scatterlists without considering the importing device's maximum DMA segment size. When an entry exceeds that limit, DMA_API_DEBUG reports "mapping sg segment longer than device claims to support". Patch 3 uses the importer's limit. A corresponding udmabuf fix was posted in [1]. With patch 3, an importer that keeps the 64 KiB default gets a larger buffer in several entries. Two in-tree importers require a single entry and never set a limit: tegra-vde without an IOMMU domain, and armada. Patches 1 and 2 set an unlimited segment size there. I found them by searching the importers for checks on the number of entries and on the length of the first entry. etnaviv has a fast path for single-entry buffers but already declares a 2 GiB limit. Patches 1 and 2 are valid on their own and can go through their own trees. Patch 3 should only be applied after them, and is marked stable+noautosel for that reason. Tested in QEMU only, not on real hardware: patch 3 on a custom model of the SAM9X75 Curiosity, and all three patches on xilinx-zynq-a9 with tegra-vde and armada probing from stub device tree nodes. The notes of each patch have the details. [1] https://lore.kernel.org/r/20260929054835.94118-1-kmehltretter@gmail.com/ Karl Mehltretter (3): media: tegra-vde: set an unlimited DMA segment size drm/armada: set an unlimited DMA segment size dma-buf: heaps: cma: respect the device's maximum segment size drivers/dma-buf/heaps/cma_heap.c | 14 ++++++++++---- drivers/gpu/drm/armada/armada_drv.c | 3 +++ drivers/media/platform/nvidia/tegra-vde/vde.c | 2 ++ 3 files changed, 15 insertions(+), 4 deletions(-) base-commit: fe2ec83746e501645709761605c2464a44fd2929 -- 2.53.0