[PATCH RFC 1/2] iommu/dma: skip swiotlb bounce for DMA_ATTR_MMIO in iommu_dma_map_phys

[Peng Fan (OSS)]

From: Peng Fan <peng.fan@xxxxxxx>

MMIO resources mapped via dma_map_resource() carry DMA_ATTR_MMIO. These
never need swiotlb bounce buffering, but the current code enters the
swiotlb path when the physical address is not page-aligned, then rejects
the mapping because MMIO cannot be bounced.

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

Fixes: f9374de14c0e8 ("iommu/dma: implement DMA_ATTR_MMIO for iommu_dma_(un)map_phys()")
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 65d692ec7fced..26b9c2d71cd30 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1228,9 +1228,9 @@ dma_addr_t iommu_dma_map_phys(struct device *dev, phys_addr_t phys, size_t size,
 	 * If both the physical buffer start address and size are page aligned,
 	 * we don't need to use a bounce page.
 	 */
-	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 DMA_MAPPING_ERROR;
 
 		phys = iommu_dma_map_swiotlb(dev, phys, size, dir, attrs);

-- 
2.34.1