[PATCH V1 net-next 5/5] net: ena: Add devlink documentation

[David Arinzon <darinzon@amazon.com>]

Update the documentation with a devlink section, the
added files, as well as large LLQ enablement.

Signed-off-by: Shay Agroskin <shayagr@amazon.com>
Signed-off-by: David Arinzon <darinzon@amazon.com>
---
 .../device_drivers/ethernet/amazon/ena.rst    | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/Documentation/networking/device_drivers/ethernet/amazon/ena.rst b/Documentation/networking/device_drivers/ethernet/amazon/ena.rst
index 8bcb173e0353..1229732a8c91 100644
--- a/Documentation/networking/device_drivers/ethernet/amazon/ena.rst
+++ b/Documentation/networking/device_drivers/ethernet/amazon/ena.rst
@@ -53,6 +53,7 @@ ena_common_defs.h   Common definitions for ena_com layer.
 ena_regs_defs.h     Definition of ENA PCI memory-mapped (MMIO) registers.
 ena_netdev.[ch]     Main Linux kernel driver.
 ena_ethtool.c       ethtool callbacks.
+ena_devlink.[ch]    devlink files (see `devlink support`_ for more info)
 ena_pci_id_tbl.h    Supported device IDs.
 =================   ======================================================
 
@@ -253,6 +254,35 @@ RSS
 - The user can provide a hash key, hash function, and configure the
   indirection table through `ethtool(8)`.
 
+.. _`devlink support`:
+DEVLINK SUPPORT
+===============
+.. _`devlink`: https://www.kernel.org/doc/html/latest/networking/devlink/index.html
+
+`devlink`_ supports toggling LLQ entry size between the default 128 bytes and 256
+bytes.
+A 128 bytes entry size allows for a maximum of 96 bytes of packet header size
+which sometimes is not enough (e.g. when using tunneling).
+Increasing LLQ entry size to 256 bytes, allows a maximum header size of 224
+bytes. This comes with the penalty of reducing the number of LLQ entries in the
+TX queue by 2 (i.e. from 1024 to 512).
+
+The entry size can be toggled by enabling/disabling the large_llq_header devlink
+param and reloading the driver to make it take effect, e.g.
+
+.. code-block:: shell
+
+  sudo devlink dev param set pci/0000:00:06.0 name large_llq_header value true cmode driverinit
+  sudo devlink dev reload pci/0000:00:06.0
+
+One way to verify that the TX queue entry size has indeed increased is to check
+that the maximum TX queue depth is 512. This can be checked, for example, by
+using:
+
+.. code-block:: shell
+
+  ethtool -g [interface]
+
 DATA PATH
 =========
 
-- 
2.38.1