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[2a02:3100:b305:2001:39fa:3d24:821a:4eae]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a027741586sm315273615e9.14.2026.10.04.23.46.49 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 04 Oct 2026 23:46:49 -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 2/3] drm/armada: set an unlimited DMA segment size Date: Mon, 5 Oct 2026 08:46:39 +0200 Message-Id: <20261005064640.7776-3-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, importing a larger contiguous dma-buf reports: DMA-API: armada-drm armada-drm: mapping sg segment longer than device claims to support [len=1228800] [max=65536] armada_gem_map_import() also needs the buffer as one entry. An exporter that respects the 64 KiB claim has to split a larger buffer, and the import fails with "dma_buf_map_attachment() returned an (unsupported) scattered list". Set the maximum segment size to UINT_MAX. Verified with a QEMU stub. Not tested on real hardware. Fixes: 96f60e37dc66 ("DRM: Armada: Add Armada DRM 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 LCD controller probed from a stub device tree node, so all registers read 0. A test module registered the armada-drm platform device, because nothing in mainline registers it. Creating a framebuffer from an imported 1228800-byte CMA heap buffer works before and after this patch, with one segment-length report before and none after. With patch 3 alone it fails. With patches 2 and 3 it works. drivers/gpu/drm/armada/armada_drv.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/gpu/drm/armada/armada_drv.c b/drivers/gpu/drm/armada/armada_drv.c index cae25ad66c74..42498fc77e54 100644 --- a/drivers/gpu/drm/armada/armada_drv.c +++ b/drivers/gpu/drm/armada/armada_drv.c @@ -6,6 +6,7 @@ #include #include #include +#include #include #include #include @@ -101,6 +102,8 @@ static int armada_drm_bind(struct device *dev) dev_set_drvdata(dev, &priv->drm); + dma_set_max_seg_size(dev, UINT_MAX); + /* Mode setting support */ drm_mode_config_init(&priv->drm); priv->drm.mode_config.min_width = 320; -- 2.53.0