net: tso: Introduce tso_dma_map and helpers

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>

0 files changed, 0 insertions, 0 deletions