[PATCH 0/3] support setting lanes

[Ajit Khaparde]

On Mon, Mar 18, 2024 at 2:42 PM Stephen Hemminger
<stephen at networkplumber.org> wrote:
>
> On Mon, 18 Mar 2024 14:26:33 -0700
> Damodharam Ammepalli <damodharam.ammepalli at broadcom.com> wrote:
>
> > On Mon, Mar 18, 2024 at 7:56 AM Thomas Monjalon <thomas at monjalon.net> wrote:
> > >
> > > 12/03/2024 08:52, Dengdui Huang:
> > > > 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.
> > > > When use different lanes, the port cannot be up.
> > >
> > > I'm not sure what you are referring to.
> > > I suppose it is not PCI lanes.
> > > Please could you link to an explanation of how a port is split in lanes?
> > > Which hardware does this?
> > >
> > >
> > >
> > This is a snapshot of 100Gb that the latest BCM576xx supports.
> > 100Gb (NRZ: 25G per lane, 4 lanes) link speed
> > 100Gb (PAM4-56: 50G per lane, 2 lanes) link speed
> > 100Gb (PAM4-112: 100G per lane, 1 lane) link speed
> >
> > Let the user feed in lanes=< integer value> and the NIC driver decides
> > the matching combination speed x lanes that works. In future if a new speed
> > is implemented with more than 8 lanes, there wouldn't be a need
> > to touch this speed command. Using separate lane command would
> > be a better alternative to support already shipped products and only new
> > drivers would consider this lanes configuration, if applicable.
> >
>
> The DPDK does not need more driver specific knobs.
> Shouldn't the PMD be able to auto negotiate the speed?
Yes. Its possible to auto negotiate. And that's the default.
Even for the lane count, a default number can be arrived at.

> What does Linux do?
ethtool has been extended a while ago to allow configuring the number
of lanes along with speed and other settings.
But as usual, autoneg is possible.
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