[PATCH] doc: announce header split deprecation

[xuan.ding@intel.com]

From: Xuan Ding <xuan.ding@intel.com>

RTE_ETH_RX_OFFLOAD_HEADER_SPLIT offload was introduced some time ago to
substitute bit-field header_split in struct rte_eth_rxmode. It allows
to enable header split offload with the header size controlled using
split_hdr_size in the same structure.

Right now, no single PMD actually supports RTE_ETH_RX_OFFLOAD_HEADER_SPLIT
with above definition. Many examples and test apps initialize the field
to 0 explicitly. The most of drivers simply ignore split_hdr_size since
the offload is not advertised, but some double-check that its value is 0.

So the RTE_ETH_RX_OFFLOAD_HEADER_SPLIT and split_header_size field
will be removed in DPDK 22.11.

Signed-off-by: Xuan Ding <xuan.ding@intel.com>
---
 doc/guides/rel_notes/deprecation.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
index 4e5b23c53d..b8114f29ed 100644
--- a/doc/guides/rel_notes/deprecation.rst
+++ b/doc/guides/rel_notes/deprecation.rst
@@ -125,3 +125,7 @@ Deprecation Notices
   applications should be updated to use the ``dmadev`` library instead,
   with the underlying HW-functionality being provided by the ``ioat`` or
   ``idxd`` dma drivers
+
+* ethdev: After bit-field header split was removed, the ``RTE_ETH_RX_OFFLOAD_HEADER_SPLIT``
+offload and the ``split_hdr_size`` field in structure ``rte_eth_rxmode`` to enable header
+split offload are not supported in any PMDs. They will be removed in DPDK 22.11.
-- 
2.17.1