From: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Sometimes the user needs to split each entry on the mapped scatter list
due to DMA length constrains. This helper returns a number of entities
assuming that each of them is not bigger than supplied maximum length.
Signed-off-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
---
include/linux/scatterlist.h | 1 +
lib/scatterlist.c | 25 +++++++++++++++++++++++++
2 files changed, 26 insertions(+)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index cb3c8fe..d199667 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -243,6 +243,7 @@ static inline void *sg_virt(struct scatterlist *sg)
int sg_nents(struct scatterlist *sg);
int sg_nents_for_len(struct scatterlist *sg, u64 len);
+int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len);
struct scatterlist *sg_next(struct scatterlist *);
struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
void sg_init_table(struct scatterlist *, unsigned int);
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 004fc70..5b75a21 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -90,6 +90,31 @@ int sg_nents_for_len(struct scatterlist *sg, u64 len)
EXPORT_SYMBOL(sg_nents_for_len);
/**
+ * sg_nents_for_dma - return count of DMA-capable entries in scatterlist
+ * @sgl: The scatterlist
+ * @sglen: The current number of entries
+ * @len: The maximum length of DMA-capable block
+ *
+ * Description:
+ * Determines the number of entries in @sgl which would be permitted in
+ * DMA-capable transfer if list had been split accordingly, taking into
+ * account chaining as well.
+ *
+ * Returns:
+ * the number of sgl entries needed
+ *
+ **/
+int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len)
+{
+ struct scatterlist *sg;
+ int i, nents = 0;
+
+ for_each_sg(sgl, sg, sglen, i)
+ nents += DIV_ROUND_UP(sg_dma_len(sg), len);
+ return nents;
+}
+
+/**
* sg_last - return the last scatterlist entry in a list
* @sgl: First entry in the scatterlist
* @nents: Number of entries in the scatterlist
--
2.9.3
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