[RFC net-next 01/10] net: tso: Introduce tso_dma_map

[Joe Damato <joe@dama.to>]

Add struct tso_dma_map to tso.h for tracking DMA addresses of mapped
GSO payload data.

The struct combines DMA mapping storage (linear_dma, frags[]) with
iterator state (frag_idx, offset), allowing drivers to walk pre-mapped
DMA regions linearly. Helpers to initialize and operate on this struct
will be added in the next commit.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Joe Damato <joe@dama.to>
---
 include/net/tso.h | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/include/net/tso.h b/include/net/tso.h
index e7e157ae0526..9a508e60ee19 100644
--- a/include/net/tso.h
+++ b/include/net/tso.h
@@ -3,6 +3,7 @@
 #define _TSO_H
 
 #include <linux/skbuff.h>
+#include <linux/dma-mapping.h>
 #include <net/ip.h>
 
 #define TSO_HEADER_SIZE		256
@@ -28,4 +29,40 @@ void tso_build_hdr(const struct sk_buff *skb, char *hdr, struct tso_t *tso,
 void tso_build_data(const struct sk_buff *skb, struct tso_t *tso, int size);
 int tso_start(struct sk_buff *skb, struct tso_t *tso);
 
+/**
+ * struct tso_dma_map - DMA mapping state for GSO payload
+ * @dev: device used for DMA mapping
+ * @skb: the GSO skb being mapped
+ * @hdr_len: per-segment header length
+ * @frag_idx: current region (-1 = linear, 0..nr_frags-1 = frag)
+ * @offset: byte offset within current region
+ * @linear_dma: DMA address of the linear payload (after headers)
+ * @linear_len: length of the linear payload
+ * @nr_frags: number of frags successfully DMA-mapped
+ * @frags: per-frag DMA address and length
+ *
+ * Struct that DMA-maps the payload regions of a GSO skb
+ * (linear data + frags) upfront, then provides iteration to yield
+ * (dma_addr, chunk_len) pairs bounded by region boundaries.
+ *
+ * Drivers set dma_unmap_len on the first descriptor touching each DMA
+ * mapping; the completion path unmaps via per-descriptor dma_unmap_len.
+ */
+struct tso_dma_map {
+	struct device		*dev;
+	const struct sk_buff	*skb;
+	unsigned int		hdr_len;
+	/* Iterator state */
+	int			frag_idx;
+	unsigned int		offset;
+	/* Pre-mapped regions */
+	dma_addr_t		linear_dma;
+	unsigned int		linear_len;
+	unsigned int		nr_frags;
+	struct {
+		dma_addr_t	dma;
+		unsigned int	len;
+	} frags[MAX_SKB_FRAGS];
+};
+
 #endif	/* _TSO_H */
-- 
2.52.0