Re: [PATCH 0/3] support setting lanes

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 18 Mar 2024 14:26:33 -0700
Damodharam Ammepalli <damodharam.ammepalli@broadcom.com> wrote:

> On Mon, Mar 18, 2024 at 7:56 AM Thomas Monjalon <thomas@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?
What does Linux do?