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This patch introduces the DMA_ATTR_MMIO attribute to mark DMA buffers that reside in memory-mapped I/O (MMIO) regions, such as device BARs exposed through the host bridge, which are accessible for peer-to-peer (P2P) DMA. This attribute is especially useful for exporting device memory to other devices for DMA without CPU involvement, and avoids unnecessary or potentially detrimental CPU cache maintenance calls. DMA_ATTR_MMIO is supposed to provide dma_map_resource() functionality without need to call to special function and perform branching when processing generic containers like bio_vec by the callers. Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Signed-off-by: Leon Romanovsky <leonro@nvidia.com> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> Link: https://lore.kernel.org/r/6f058ec395c5348014860dbc2eed348c17975843.1757423202.git.leonro@nvidia.com