crypto: qce - Hold back a block of data to be transferred as part of final

If the available data to transfer is exactly a multiple of block size, save
the last block to be transferred in qce_ahash_final (with the last block
bit set) if this is indeed the end of data stream. If not this saved block
will be transferred as part of next update. If this block is not held back
and if this is indeed the end of data stream, the digest obtained will be
wrong since qce_ahash_final will see that rctx->buflen is 0 and return
doing nothing which in turn means that a digest will not be copied to the
destination result buffer.  qce_ahash_final cannot be made to alter this
behavior and allowed to proceed if rctx->buflen is 0 because the crypto
engine BAM does not allow for zero length transfers.
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/qce/sha.c

@@ -216,6 +216,25 @@ static int qce_ahash_update(struct ahash_request *req)
 
 	/* calculate how many bytes will be hashed later */
 	hash_later = total % blocksize;
+
+	/*
+	 * At this point, there is more than one block size of data.  If
+	 * the available data to transfer is exactly a multiple of block
+	 * size, save the last block to be transferred in qce_ahash_final
+	 * (with the last block bit set) if this is indeed the end of data
+	 * stream. If not this saved block will be transferred as part of
+	 * next update. If this block is not held back and if this is
+	 * indeed the end of data stream, the digest obtained will be wrong
+	 * since qce_ahash_final will see that rctx->buflen is 0 and return
+	 * doing nothing which in turn means that a digest will not be
+	 * copied to the destination result buffer.  qce_ahash_final cannot
+	 * be made to alter this behavior and allowed to proceed if
+	 * rctx->buflen is 0 because the crypto engine BAM does not allow
+	 * for zero length transfers.
+	 */
+	if (!hash_later)
+		hash_later = blocksize;
+
 	if (hash_later) {
 		unsigned int src_offset = req->nbytes - hash_later;
 		scatterwalk_map_and_copy(rctx->buf, req->src, src_offset,