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Add struct tso_dma_map to tso.h for tracking DMA addresses of mapped GSO payload data and tso_dma_map_completion_state. The tso_dma_map combines DMA mapping storage with iterator state, allowing drivers to walk pre-mapped DMA regions linearly. Includes fields for the DMA IOVA path (iova_state, iova_offset, total_len) and a fallback per-region path (linear_dma, frags[], frag_idx, offset). The tso_dma_map_completion_state makes the IOVA completion state opaque for drivers. Drivers are expected to allocate this and use the added helpers to update the completion state. Adds skb_frag_phys() to skbuff.h, returning the physical address of a paged fragment's data, which is used by the tso_dma_map helpers introduced in this commit described below. The added TSO DMA map helpers are: tso_dma_map_init(): DMA-maps the linear payload region and all frags upfront. Prefers the DMA IOVA API for a single contiguous mapping with one IOTLB sync; falls back to per-region dma_map_phys() otherwise. Returns 0 on success, cleans up partial mappings on failure. tso_dma_map_cleanup(): Handles both IOVA and fallback teardown paths. tso_dma_map_count(): counts how many descriptors the next N bytes of payload will need. Returns 1 if IOVA is used since the mapping is contiguous. tso_dma_map_next(): yields the next (dma_addr, chunk_len) pair. On the IOVA path, each segment is a single contiguous chunk. On the fallback path, indicates when a chunk starts a new DMA mapping so the driver can set dma_unmap_len on that descriptor for completion-time unmapping. tso_dma_map_completion_save(): updates the completion state. Drivers will call this at xmit time. tso_dma_map_complete(): tears down the mapping at completion time and returns true if the IOVA path was used. If it was not used, this is a no-op and returns false. Suggested-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Joe Damato <joe@dama.to> Link: https://patch.msgid.link/20260408230607.2019402-2-joe@dama.to Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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