[PATCH] net/mlx5: fix modify field action operation restriction

[Maayan Kashani <mkashani@nvidia.com>]

Update DV flow engine modify field validation:
- Reject 'add' and 'sub' operations when source field is not VALUE
  or POINTER in DV flow engine.

Update documentation to clarify operation support:
- 'set' operation is supported in all modes
- 'add' operation with VALUE/POINTER source fields is
  supported in DV/HWS mode.
- Specify relevant HW supporting packet header as 'src' field.
- List supported 'dst' fields.

Fixes: 641dbe4fb053 ("net/mlx5: support modify field flow action")
Cc: stable@dpdk.org

Signed-off-by: Maayan Kashani <mkashani@nvidia.com>
Acked-by: Dariusz Sosnowski <dsosnowski@nvidia.com>
---
 doc/guides/nics/mlx5.rst        | 23 ++++++++++++++++++++++-
 drivers/net/mlx5/mlx5_flow_dv.c |  7 +++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index fde98ae9936..3c13e586dd9 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -3083,7 +3083,28 @@ DPDK       21.02
 Limitations
 ^^^^^^^^^^^
 
-#. Supports the 'set' and 'add' operations for ``RTE_FLOW_ACTION_TYPE_MODIFY_FIELD`` action.
+#. Supports the 'set' operation for ``RTE_FLOW_ACTION_TYPE_MODIFY_FIELD`` in all flow engines.
+
+#. Supports the 'add' operation with 'src' field of type
+   ``RTE_FLOW_FIELD_VALUE`` or ``RTE_FLOW_FIELD_POINTER`` with both :ref:`HW steering <mlx5_hws>`
+   and DV flow engine (``dv_flow_en=1``).
+
+   HW steering flow engine, starting with ConnectX-7 and BlueField-3,
+   supports packet header fields in 'src' field.
+
+   'dst' field can be any of the following:
+
+   - ``RTE_FLOW_FIELD_IPV4_TTL``
+   - ``RTE_FLOW_FIELD_IPV6_HOPLIMIT``
+   - ``RTE_FLOW_FIELD_TCP_SEQ_NUM``
+   - ``RTE_FLOW_FIELD_TCP_ACK_NUM``
+   - ``RTE_FLOW_FIELD_TAG``
+   - ``RTE_FLOW_FIELD_META``
+   - ``RTE_FLOW_FIELD_FLEX_ITEM``
+   - ``RTE_FLOW_FIELD_TCP_DATA_OFFSET``
+   - ``RTE_FLOW_FIELD_IPV4_IHL``
+   - ``RTE_FLOW_FIELD_IPV4_TOTAL_LEN``
+   - ``RTE_FLOW_FIELD_IPV6_PAYLOAD_LEN``
 
 #. In template tables of group 0, the modify action must be fully masked.
 
diff --git a/drivers/net/mlx5/mlx5_flow_dv.c b/drivers/net/mlx5/mlx5_flow_dv.c
index f765f941162..95ca57e8c46 100644
--- a/drivers/net/mlx5/mlx5_flow_dv.c
+++ b/drivers/net/mlx5/mlx5_flow_dv.c
@@ -5642,6 +5642,13 @@ flow_dv_validate_action_modify_field(struct rte_eth_dev *dev,
 	}
 	if (src_data->field != RTE_FLOW_FIELD_VALUE &&
 	    src_data->field != RTE_FLOW_FIELD_POINTER) {
+		if (conf->operation != RTE_FLOW_MODIFY_SET)
+			return rte_flow_error_set(error, ENOTSUP,
+						  RTE_FLOW_ERROR_TYPE_ACTION_CONF,
+						  &conf->operation,
+						  "modify field action type add is not"
+						  " supported when src field type is"
+						  " not value/pointer");
 		if (root)
 			return rte_flow_error_set(error, ENOTSUP,
 					RTE_FLOW_ERROR_TYPE_ACTION, action,
-- 
2.21.0