[dpdk-dev] [PATCH v4] doc: update hairpin data buffer size config

[Bing Zhao <bingz@mellanox.com>]

This patch updates the MLX5 PMD and release notes documentations.
Adding the guideline for hairpin data buffer size configuration.

Signed-off-by: Bing Zhao <bingz@mellanox.com>
Acked-by: Ori Kam <orika@mellanox.com>
---
v2: update the range description of hairpin data buffer size
v3: correct the minimum value of the range
v4: correct some typos and grammatical errors
---
 doc/guides/nics/mlx5.rst               | 16 ++++++++++++++++
 doc/guides/rel_notes/release_20_05.rst |  1 +
 2 files changed, 17 insertions(+)

diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index 759d0ac..51b5d47 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -99,6 +99,7 @@ Features
 - Support for multiple rte_flow groups.
 - Per packet no-inline hint flag to disable packet data copying into Tx descriptors.
 - Hardware LRO.
+- Hairpin.
 
 Limitations
 -----------
@@ -786,6 +787,21 @@ Run-time configuration
   If this parameter is not specified, by default PMD will set
   the smallest value supported by HW.
 
+- ``hp_buf_log_sz`` parameter [int]
+
+  The total data buffer size of a hairpin queue (logarithmic form), in bytes.
+  PMD will set the data buffer size to 2 ** ``hp_buf_log_sz``, both for RX & TX.
+  The capacity of the value is specified by the firmware and the initialization
+  will get a failure if it is out of scope.
+  The range of the value is from 11 to 19 right now, and the supported frame
+  size of a single packet for hairpin is from 512B to 128KB. It might change if
+  different firmware release is being used. By using a small value, it could
+  reduce memory consumption but not work with a large frame. If the value is
+  too large, the memory consumption will be high and some potential performance
+  degradation will be introduced.
+  By default, the PMD will set this value to 16, which means that 9KB jumbo
+  frames will be supported.
+
 .. _mlx5_firmware_config:
 
 Firmware configuration
diff --git a/doc/guides/rel_notes/release_20_05.rst b/doc/guides/rel_notes/release_20_05.rst
index 1e5304d..d43aa2e 100644
--- a/doc/guides/rel_notes/release_20_05.rst
+++ b/doc/guides/rel_notes/release_20_05.rst
@@ -78,6 +78,7 @@ New Features
 
   * Added support for matching on IPv4 Time To Live and IPv6 Hop Limit.
   * Added support for creating Relaxed Ordering Memory Regions.
+  * Added support for configuring Hairpin queue data buffer size.
   * Added support for jumbo frame size (9K MTU) in Multi-Packet RQ mode.
   * Optimized the memory consumption of flow.
 
-- 
1.8.3.1