[PATCH v2] 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 per-port 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. After DPDK 22.11 LTS, the
RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT can still be used for per-queue Rx
packet split offload, which is configured by rte_eth_rxseg_split.

Signed-off-by: Xuan Ding <xuan.ding@intel.com>
Acked-by: Ray Kinsella <mdr@ashroe.eu>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Acked-by: Ferruh Yigit <ferruh.yigit@xilinx.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
---
v2:
* Refine doc to mention remained RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT.
---
 doc/guides/rel_notes/deprecation.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
index 1e5e532e60..ae37559275 100644
--- a/doc/guides/rel_notes/deprecation.rst
+++ b/doc/guides/rel_notes/deprecation.rst
@@ -158,3 +158,10 @@ 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: Since no single PMD supports ``RTE_ETH_RX_OFFLOAD_HEADER_SPLIT`` offload
+and the ``split_hdr_size`` field in structure ``rte_eth_rxmode`` to enable per-port
+header split as they were designed, they will be removed in DPDK 22.11.
+After DPDK 22.11 LTS, the ``RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT`` can still be
+used for per-queue Rx packet split offload, and it is configured
+by ``rte_eth_rxseg_split``.
-- 
2.17.1