Re: [PATCH 0/3] support setting lanes

[Jerin Jacob <jerinjacobk@gmail.com>]

On Fri, Mar 22, 2024 at 7:21 PM Thomas Monjalon <thomas@monjalon.net> wrote:
>
> 22/03/2024 06:51, Jerin Jacob:
> > On Fri, Mar 22, 2024 at 10:56 AM Ajit Khaparde
> > <ajit.khaparde@broadcom.com> wrote:
> > >
> > > On Thu, Mar 21, 2024 at 9:39 PM Jerin Jacob <jerinjacobk@gmail.com> wrote:
> > > >
> > > > On Fri, Mar 22, 2024 at 7:58 AM huangdengdui <huangdengdui@huawei.com> wrote:
> > > > >
> > > > >
> > > > >

> > > > For example, If FW configures, 100G port as 100GBASE-SR2 then two
> > > > ethdev(port 0 and port1) will show up.
> > > > Now, assume if we expose this API and Can end user configure port 1 as
> > > > 25G lines if so,
> > > > a) What happens to port0 and it states?
> > > There should be no impact to port0.
> > >
> > > > b) Will port2, port3 will show up after issuing this API(As end user
> > > > configured 25Gx4 for 100G)? Will application needs to hotplug to get
> > > > use ports.
> > > No. The port count does not change. Nor does the number of PCI
> > > functions seen by the host. Unless designed otherwise.
> > >
> > > Changing the lane count does not change anything in physical terms.
> > > What changes is the modulation or the signaling scheme.
> > > The number of lanes which can be supported is determined by
> > > the PHY itself and the cables used and needs to be negotiated appropriately
> > > with the remote partner - which is just like using forced Ethernet Speed
> > > instead of auto-negotiated speeds.
>
> Thanks for the explanation Ajit.
>
> > OK. It looks like platform independent then. At least cnxk driver, End
> > user cannot simplify change the line config parameters
> > while traffic is active also, it looks like other drivers need to have
> > SerDes training with remote partner while reconfiguring it.
> >
> > At least on cnxk platform, 25Gx4 on 100G will show as 4 ethdev devices.
>
> That's a strange behaviour.
> Why showing 4 ports which are not independent?

I checked SerDes + NIC configuration again. It supports both modes.
Show up as One port vs four ports.

>
> > Having said that, If other NICs support this feature without
> > disturbing current port states, I don't have an objection to this API.
>
>
>