[PATCH v4 3/4] hash: implement RSS hash key generation API

[Vladimir Medvedkin <vladimir.medvedkin@intel.com>]

This patch implements Toeplitz hash key generation function using the new
polynomial generation function.

Signed-off-by: Vladimir Medvedkin <vladimir.medvedkin@intel.com>
---
 doc/guides/rel_notes/release_24_11.rst |  3 +++
 lib/hash/rte_thash.c                   | 23 ++++++++++++++++++-----
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/doc/guides/rel_notes/release_24_11.rst b/doc/guides/rel_notes/release_24_11.rst
index fa4822d928..9d00a2e1c2 100644
--- a/doc/guides/rel_notes/release_24_11.rst
+++ b/doc/guides/rel_notes/release_24_11.rst
@@ -247,6 +247,9 @@ New Features
   Added ability for node to advertise and update multiple xstat counters,
   that can be retrieved using ``rte_graph_cluster_stats_get``.
 
+* **Added RSS hash key generating API.**
+  A new function ``rte_thash_gen_key`` is provided to modify the RSS hash key
+  to achieve better traffic distribution with RSS.
 
 Removed Items
 -------------
diff --git a/lib/hash/rte_thash.c b/lib/hash/rte_thash.c
index da35aec860..336c228e64 100644
--- a/lib/hash/rte_thash.c
+++ b/lib/hash/rte_thash.c
@@ -827,11 +827,24 @@ int
 rte_thash_gen_key(uint8_t *key, size_t key_len, size_t reta_sz_log,
 	uint32_t entropy_start, size_t entropy_sz)
 {
-	RTE_SET_USED(key);
-	RTE_SET_USED(key_len);
-	RTE_SET_USED(reta_sz_log);
-	RTE_SET_USED(entropy_start);
-	RTE_SET_USED(entropy_sz);
+	size_t i, end, start;
+
+	/* define lfsr sequence range*/
+	end = entropy_start + entropy_sz + TOEPLITZ_HASH_LEN - 1;
+	start = end - (entropy_sz + reta_sz_log - 1);
+
+	if ((key == NULL) || (key_len * CHAR_BIT < entropy_start + entropy_sz) ||
+			(entropy_sz < reta_sz_log) || (reta_sz_log > TOEPLITZ_HASH_LEN))
+		return -EINVAL;
+
+	struct thash_lfsr *lfsr = alloc_lfsr(reta_sz_log);
+	if (lfsr == NULL)
+		return -ENOMEM;
+
+	for (i = start; i < end; i++)
+		set_bit(key, get_bit_lfsr(lfsr), i);
+
+	free_lfsr(lfsr);
 
 	return 0;
 }
-- 
2.43.0