[PATCH] doc/mlx5: document modify field limitation on group 0

[Maayan Kashani <mkashani@nvidia.com>]

Document that on the root table, two sequential MODIFY_FIELD actions
where the second uses a field modified by the first as src are not
supported: the second action is handled before the first change is
applied. Only immediate src types (VALUE/POINTER) are allowed on
group 0 for sync HWS non-template and DV flows.

Signed-off-by: Maayan Kashani <mkashani@nvidia.com>
---
 doc/guides/nics/mlx5.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index 9b035b878e0..aa751669444 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -3425,6 +3425,12 @@ Limitations
 
 #. In template tables of group 0, the modify action must be fully masked.
 
+#. On group 0 (root table), when using sync API, two sequential
+   ``RTE_FLOW_ACTION_TYPE_MODIFY_FIELD`` actions where the first modifies a
+   packet or metadata field and the second uses that field as ``src`` are not
+   supported. On the root table the second action is handled before the first
+   change is applied, so the source still reads the original field value.
+
 #. Modification of an arbitrary place in a packet via
    the special ``RTE_FLOW_FIELD_START`` field ID is not supported.
 
-- 
2.21.0