Re: [PATCH 02/13] IB/core: allow passing mapping an offset into the SG in ib_map_mr_sg

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@@ -1593,6 +1592,7 @@ EXPORT_SYMBOL(ib_map_mr_sg);
   * @mr:            memory region
   * @sgl:           dma mapped scatterlist
   * @sg_nents:      number of entries in sg
+ * @sg_offset:     offset in byes into sg
   * @set_page:      driver page assignment function pointer
   *
   * Core service helper for drivers to convert the largest
@@ -1603,10 +1603,8 @@ EXPORT_SYMBOL(ib_map_mr_sg);
   * Returns the number of sg elements that were assigned to
   * a page vector.
   */
-int ib_sg_to_pages(struct ib_mr *mr,
-		   struct scatterlist *sgl,
-		   int sg_nents,
-		   int (*set_page)(struct ib_mr *, u64))
+int ib_sg_to_pages(struct ib_mr *mr, struct scatterlist *sgl, int sg_nents,
+		unsigned int sg_offset, int (*set_page)(struct ib_mr *, u64))
  {
  	struct scatterlist *sg;
  	u64 last_end_dma_addr = 0;
@@ -1618,8 +1616,8 @@ int ib_sg_to_pages(struct ib_mr *mr,
  	mr->length = 0;

  	for_each_sg(sgl, sg, sg_nents, i) {
-		u64 dma_addr = sg_dma_address(sg);
-		unsigned int dma_len = sg_dma_len(sg);
+		u64 dma_addr = sg_dma_address(sg) + sg_offset;
+		unsigned int dma_len = sg_dma_len(sg) - sg_offset;
  		u64 end_dma_addr = dma_addr + dma_len;
  		u64 page_addr = dma_addr & page_mask;

@@ -1652,6 +1650,8 @@ next_page:
  		mr->length += dma_len;
  		last_end_dma_addr = end_dma_addr;
  		last_page_off = end_dma_addr & ~page_mask;
+
+		sg_offset = 0;
  	}

This looks wrong...

The SG offset should not be taken into account in the address
translation vector that is given to the HW. The sg_offset needs to
be accounted in the mr->iova:

mr->iova = sg_dma_address(&sgl[0]) + sg_offset;

I think the page mappings should stay as the are.
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