Re: [PATCH v4 09/16] dma-mapping: handle MMIO flow in dma_map|unmap_page
From: Jason Gunthorpe <jgg@nvidia.com>
Date: 2025-08-28 15:17:42
Also in:
linux-block, linux-doc, linux-iommu, linux-mm, linux-nvme, linux-trace-kernel, lkml, rust-for-linux, virtualization, xen-devel
On Tue, Aug 19, 2025 at 08:36:53PM +0300, Leon Romanovsky wrote:
From: Leon Romanovsky <leonro@nvidia.com> Extend base DMA page API to handle MMIO flow and follow existing dma_map_resource() implementation to rely on dma_map_direct() only to take DMA direct path.
I would reword this a little bit too dma-mapping: implement DMA_ATTR_MMIO for dma_(un)map_page_attrs() Make dma_map_page_attrs() and dma_map_page_attrs() respect DMA_ATTR_MMIO. DMA_ATR_MMIO makes the functions behave the same as dma_(un)map_resource(): - No swiotlb is possible - Legacy dma_ops arches use ops->map_resource() - No kmsan - No arch_dma_map_phys_direct() The prior patches have made the internl funtions called here support DMA_ATTR_MMIO. This is also preparation for turning dma_map_resource() into an inline calling dma_map_phys(DMA_ATTR_MMIO) to consolidate the flows.
quoted hunk ↗ jump to hunk
@@ -166,14 +167,25 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page, return DMA_MAPPING_ERROR; if (dma_map_direct(dev, ops) || - arch_dma_map_phys_direct(dev, phys + size)) + (!is_mmio && arch_dma_map_phys_direct(dev, phys + size))) addr = dma_direct_map_phys(dev, phys, size, dir, attrs);
PPC is the only user of arch_dma_map_phys_direct() and it looks like it should be called on MMIO memory. Seems like another inconsistency with map_resource. I'd leave it like the above though for this series.
else if (use_dma_iommu(dev))
addr = iommu_dma_map_phys(dev, phys, size, dir, attrs);
- else
+ else if (is_mmio) {
+ if (!ops->map_resource)
+ return DMA_MAPPING_ERROR;Probably written like: if (ops->map_resource) addr = ops->map_resource(dev, phys, size, dir, attrs); else addr = DMA_MAPPING_ERROR; As I think some of the design here is to run the trace even on the failure path? Otherwise looks OK Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Jason