I still don't think it is appropriate for the UAPI to be defined in
terms of lanes. I would prefer to see it defined in terms of signal
modulation (for which multiple could conceivably exist for a given
lane configuration, even though no such ambiguity exists for today's
defined modes). Better still would be to define the UAPI in terms of
the absolute link mode enum index (with the modes that are not
compatible with the presently installed media type being rejected).

Regards,
Edwin Peer

On Wed, Jan 6, 2021 at 5:08 AM Danielle Ratson <danieller@mellanox.com> wrote:
>
> From: Danielle Ratson <danieller@nvidia.com>
>
> Some speeds can be achieved with different number of lanes. For example,
> 100Gbps can be achieved using two lanes of 50Gbps or four lanes of
> 25Gbps. This patch set adds a new selector that allows ethtool to
> advertise link modes according to their number of lanes and also force a
> specific number of lanes when autonegotiation is off.
>
> Advertising all link modes with a speed of 100Gbps that use two lanes:
>
> $ ethtool -s swp1 speed 100000 lanes 2 autoneg on
>
> Forcing a speed of 100Gbps using four lanes:
>
> $ ethtool -s swp1 speed 100000 lanes 4 autoneg off
>
> Patch set overview:
>
> Patch #1 allows user space to configure the desired number of lanes.
>
> Patch #2-#3 adjusts ethtool to dump to user space the number of lanes
> currently in use.
>
> Patches #4-#6 add support for lanes configuration in mlxsw.
>
> Patch #7 adds a selftest.
>
> v2:
>         * Patch #1: Remove ETHTOOL_LANES defines and simply use a number
>           instead.
>         * Patches #2,#6: Pass link mode from driver to ethtool instead
>         * of the parameters themselves.
>         * Patch #5: Add an actual width field for spectrum-2 link modes
>           in order to set the suitable link mode when lanes parameter is
>           passed.
>         * Patch #6: Changed lanes to be unsigned in
>           'struct link_mode_info'.
>         * Patch #7: Remove the test for recieving max_width when lanes
>         * is not set by user. When not setting lanes, we don't promise
>           anything regarding what number of lanes will be chosen.
>
> Danielle Ratson (7):
>   ethtool: Extend link modes settings uAPI with lanes
>   ethtool: Get link mode in use instead of speed and duplex parameters
>   ethtool: Expose the number of lanes in use
>   mlxsw: ethtool: Remove max lanes filtering
>   mlxsw: ethtool: Add support for setting lanes when autoneg is off
>   mlxsw: ethtool: Pass link mode in use to ethtool
>   net: selftests: Add lanes setting test
>
>  Documentation/networking/ethtool-netlink.rst  |  12 +-
>  .../net/ethernet/mellanox/mlxsw/spectrum.h    |  13 +-
>  .../mellanox/mlxsw/spectrum_ethtool.c         | 168 +++++----
>  include/linux/ethtool.h                       |   5 +
>  include/uapi/linux/ethtool.h                  |   4 +
>  include/uapi/linux/ethtool_netlink.h          |   1 +
>  net/ethtool/linkmodes.c                       | 321 +++++++++++-------
>  net/ethtool/netlink.h                         |   2 +-
>  .../selftests/net/forwarding/ethtool_lanes.sh | 186 ++++++++++
>  .../selftests/net/forwarding/ethtool_lib.sh   |  34 ++
>  tools/testing/selftests/net/forwarding/lib.sh |  28 ++
>  11 files changed, 570 insertions(+), 204 deletions(-)
>  create mode 100755 tools/testing/selftests/net/forwarding/ethtool_lanes.sh
>
> --
> 2.26.2
>