[PATCH RFC 2/2] iommu/dma: skip swiotlb bounce for DMA_ATTR_MMIO in dma_iova_link()

[Peng Fan (OSS)]

From: Peng Fan <peng.fan@xxxxxxx>

Same issue as the iommu_dma_map_phys() fix: MMIO resources never need
swiotlb bounce buffering, but dma_iova_link() enters the swiotlb path
when the physical address is not page-aligned, then rejects the mapping
with -EPERM.

Move the DMA_ATTR_MMIO check before the swiotlb block so the entire bounce
path is skipped for MMIO, falling through directly to __dma_iova_link()
which creates the IOMMU mapping.

Fixes: c288d657dd515 ("iommu/dma: implement DMA_ATTR_MMIO for dma_iova_link().")
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
---
 drivers/iommu/dma-iommu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 26b9c2d71cd30..6807430ee3ab0 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1998,9 +1998,9 @@ int dma_iova_link(struct device *dev, struct dma_iova_state *state,
 	if (!dev_is_dma_coherent(dev) && (attrs & DMA_ATTR_REQUIRE_COHERENT))
 		return -EOPNOTSUPP;
 
-	if (dev_use_swiotlb(dev, size, dir) &&
+	if (!(attrs & DMA_ATTR_MMIO) && dev_use_swiotlb(dev, size, dir) &&
 	    iova_unaligned(iovad, phys, size)) {
-		if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT))
+		if (attrs & DMA_ATTR_REQUIRE_COHERENT)
 			return -EPERM;
 
 		return iommu_dma_iova_link_swiotlb(dev, state, phys, offset,

-- 
2.34.1