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[2a02:3100:b305:2001:39fa:3d24:821a:4eae]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a027741586sm315273615e9.14.2026.10.04.23.46.46 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 04 Oct 2026 23:46:47 -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 1/3] media: tegra-vde: set an unlimited DMA segment size Date: Mon, 5 Oct 2026 08:46:38 +0200 Message-Id: <20261005064640.7776-2-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20261005064640.7776-1-kmehltretter@gmail.com> References: <20261005064640.7776-1-kmehltretter@gmail.com> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The driver never sets a maximum DMA segment size, so the device claims the 64 KiB default. With DMA_API_DEBUG, mapping a larger buffer reports: DMA-API: tegra-vde 6001a000.vde: mapping sg segment longer than device claims to support [len=1228800] [max=65536] Without an IOMMU domain the driver also needs each imported buffer as one entry. An exporter that respects the 64 KiB claim has to split a larger buffer, and queueing it fails with "Sparse DMA region is unsupported, please enable IOMMU". Set the maximum segment size to UINT_MAX. Verified with a QEMU stub. Not tested on real hardware. Fixes: cd6c56feb591 ("media: staging: media: Introduce NVIDIA Tegra video decoder driver") Assisted-by: LLM Signed-off-by: Karl Mehltretter --- Notes: Tested on v7.3-rc4-70-gfe2ec83746e5 with DMA_API_DEBUG on QEMU's xilinx-zynq-a9. The driver probed from a stub device tree node, so all registers read 0, and needed a test-only change to probe without a Tegra PMC. Queueing a capture buffer of 1228800-byte CMA heap buffers works before and after this patch, with 7 segment-length reports before and none after. With patch 3 alone it fails. With patches 1 and 3 it works. drivers/media/platform/nvidia/tegra-vde/vde.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/media/platform/nvidia/tegra-vde/vde.c b/drivers/media/platform/nvidia/tegra-vde/vde.c index c3097085ad9d..6a47e8ba083c 100644 --- a/drivers/media/platform/nvidia/tegra-vde/vde.c +++ b/drivers/media/platform/nvidia/tegra-vde/vde.c @@ -238,6 +238,8 @@ static int tegra_vde_probe(struct platform_device *pdev) vde->soc = of_device_get_match_data(&pdev->dev); vde->dev = dev; + dma_set_max_seg_size(dev, UINT_MAX); + vde->sxe = devm_platform_ioremap_resource_byname(pdev, "sxe"); if (IS_ERR(vde->sxe)) return PTR_ERR(vde->sxe); -- 2.53.0