ethtool: Support for FEC encoding control

As FEC settings and different FEC modes are mandatory
and configurable across various interfaces of 25G/50G/100G/40G,
the lack of FEC encoding control and reporting today is a source
for interoperability issues for many vendors

set-fec/show-fec option(s) are designed to provide control and report
the FEC encoding on the link.

$ethtool --set-fec swp1 encoding [off | RS | BaseR | auto]

Encoding: Types of encoding
Off    :  Turning off FEC
RS     :  Force RS-FEC encoding
BaseR  :  Force BaseR encoding
Auto   :  Default FEC settings for drivers, and would represent
          asking the hardware to essentially go into a best effort mode.

Here are a few examples of what we would expect if encoding=auto:
- if autoneg is on, we are  expecting FEC to be negotiated as on or off
  as long as protocol supports it
- if the hardware is capable of detecting the FEC encoding on it's
  receiver it will reconfigure its encoder to match
- in absence of the above, the configuration would be set to IEEE
  defaults.

>From our understanding, this is essentially what most hardware/driver
combinations are doing today in the absence of a way for users to
control the behavior.

$ethtool --show-fec  swp1
FEC parameters for swp1:
FEC encodings:  RS

ethtool devname output:
$ethtool swp1
Settings for swp1:
root@hpe-7712-03:~# ethtool swp18
Settings for swp18:
    Supported ports: [ FIBRE ]
    Supported link modes:   40000baseCR4/Full
                            40000baseSR4/Full
                            40000baseLR4/Full
                            100000baseSR4/Full
                            100000baseCR4/Full
                            100000baseLR4_ER4/Full
    Supported pause frame use: No
    Supports auto-negotiation: Yes
    Supported FEC modes: [RS | BaseR | None | Not reported]
    Advertised link modes:  Not reported
    Advertised pause frame use: No
    Advertised auto-negotiation: No
    Advertised FEC modes: [RS | BaseR | None | Not reported]
    Speed: 100000Mb/s
    Duplex: Full
    Port: FIBRE
    PHYAD: 106
    Transceiver: internal
    Auto-negotiation: off
    Link detected: yes

Signed-off-by: Vidya Sagar Ravipati <vidya.chowdary@gmail.com>
Signed-off-by: Dustin Byford <dustin@cumulusnetworks.com>
[code style + man page edits + commit message update]
Signed-off-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
2 files changed