diff --git a/target/linux/rockchip/patches-6.18/142-iommu-rockchip-translate-DMA-for-IOMMU-masters.patch b/target/linux/rockchip/patches-6.18/142-iommu-rockchip-translate-DMA-for-IOMMU-masters.patch
new file mode 100644
index 00000000000..044a6257263
--- /dev/null
+++ b/target/linux/rockchip/patches-6.18/142-iommu-rockchip-translate-DMA-for-IOMMU-masters.patch
@@ -0,0 +1,47 @@
+From f69d2a3b86e90f4141d45be7d234f9a5ab464fe8 Mon Sep 17 00:00:00 2001
+From: Daniel Golle <daniel@makrotopia.org>
+Date: Thu, 24 Sep 2026 17:39:45 +0100
+Subject: [PATCH] iommu/rockchip: use a translated domain for IOMMU masters
+
+The masters behind rockchip-iommu are media blocks: the display
+controller, the video codecs, the ISP and the 2D engine. They are wired
+to the IOMMU so that their buffers do not have to be physically
+contiguous. With a system-wide passthrough default, which is what
+IOMMU_DEFAULT_PASSTHROUGH gives, those masters are handed an identity
+domain instead, and every buffer has to come from CMA. A 4K frame needs
+15.8 MiB of it, so hardware decoding fails the allocation and falls back
+to software.
+
+Return IOMMU_DOMAIN_DMA from def_domain_type so these masters get a
+translated domain whatever the system default is, the way apple-dart
+does for its no-bypass configurations. Masters behind other IOMMUs are
+untouched, so a PCIe root port behind an SMMU keeps the system default
+and its performance.
+
+Signed-off-by: Daniel Golle <daniel@makrotopia.org>
+---
+ drivers/iommu/rockchip-iommu.c | 7 +++++++
+ 1 file changed, 7 insertions(+)
+
+--- a/drivers/iommu/rockchip-iommu.c
++++ b/drivers/iommu/rockchip-iommu.c
+@@ -1174,12 +1174,19 @@ static int rk_iommu_of_xlate(struct devi
+ 	return 0;
+ }
+ 
++/* An identity domain would put these media masters back onto CMA. */
++static int rk_iommu_def_domain_type(struct device *dev)
++{
++	return IOMMU_DOMAIN_DMA;
++}
++
+ static const struct iommu_ops rk_iommu_ops = {
+ 	.identity_domain = &rk_identity_domain,
+ 	.domain_alloc_paging = rk_iommu_domain_alloc_paging,
+ 	.probe_device = rk_iommu_probe_device,
+ 	.release_device = rk_iommu_release_device,
+ 	.device_group = generic_single_device_group,
++	.def_domain_type = rk_iommu_def_domain_type,
+ 	.of_xlate = rk_iommu_of_xlate,
+ 	.default_domain_ops = &(const struct iommu_domain_ops) {
+ 		.attach_dev	= rk_iommu_attach_device,