crypto: scatterwalk - Add support for calculating number of SG elements

Crypto layer only passes nbytes to encrypt but in omap-aes driver we need to
know number of SG elements to pass to dmaengine slave API.  We add function for
the same to scatterwalk library.

Signed-off-by: Joel Fernandes <joelf@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 22 insertions, 0 deletions

diff --git a/crypto/scatterwalk.c b/crypto/scatterwalk.c
index 7281b8a93ad3..79ca2278c2a3 100644
--- a/crypto/scatterwalk.c
+++ b/crypto/scatterwalk.c
@@ -124,3 +124,25 @@ void scatterwalk_map_and_copy(void *buf, struct scatterlist *sg,
         scatterwalk_done(&walk, out, 0);
 }
 EXPORT_SYMBOL_GPL(scatterwalk_map_and_copy);
+
+int scatterwalk_bytes_sglen(struct scatterlist *sg, int num_bytes)
+{
+        int offset = 0, n = 0;
+
+        /* num_bytes is too small */
+        if (num_bytes < sg->length)
+                return -1;
+
+        do {
+                offset += sg->length;
+                n++;
+                sg = scatterwalk_sg_next(sg);
+
+                /* num_bytes is too large */
+                if (unlikely(!sg && (num_bytes < offset)))
+                        return -1;
+        } while (sg && (num_bytes > offset));
+
+        return n;
+}
+EXPORT_SYMBOL_GPL(scatterwalk_bytes_sglen);