22/03/2024 06:51, Jerin Jacob: > On Fri, Mar 22, 2024 at 10:56 AM Ajit Khaparde > <ajit.khapa...@broadcom.com> wrote: > > > > On Thu, Mar 21, 2024 at 9:39 PM Jerin Jacob <jerinjac...@gmail.com> wrote: > > > > > > On Fri, Mar 22, 2024 at 7:58 AM huangdengdui <huangdeng...@huawei.com> > > > wrote: > > > > > > > > > > > > > > > > On 2024/3/21 16:28, Thomas Monjalon wrote: > > > > > 21/03/2024 03:02, huangdengdui: > > > > >> > > > > >> On 2024/3/20 20:31, Ferruh Yigit wrote: > > > > >>> On 3/18/2024 9:26 PM, Damodharam Ammepalli wrote: > > > > >>>> On Mon, Mar 18, 2024 at 7:56 AM Thomas Monjalon > > > > >>>> <tho...@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. > > > > >>>> > > > > >>> > > > > >>> As far as I understand, lane is related to the physical layer of the > > > > >>> NIC, there are multiple copies of transmitter, receiver, modulator > > > > >>> HW > > > > >>> block and each set called as a 'lane' and multiple lanes work > > > > >>> together > > > > >>> to achieve desired speed. (please correct me if this is wrong). > > > > >>> > > > > >>> Why not just configuring the speed is not enough? Why user needs to > > > > >>> know > > > > >>> the detail and configuration of the lanes? > > > > >>> Will it work if driver/device configure the "speed x lane" > > > > >>> internally > > > > >>> for the requested speed? > > > > >>> > > > > >>> Is there a benefit to force specific lane count for a specific speed > > > > >>> (like power optimization, just a wild guess)? > > > > >>> > > > > >>> > > > > >>> And +1 for auto-negotiation if possible. > > > > >> > > > > >> As you said above,，multiple lanes work together to achieve desired > > > > >> speed. > > > > >> For example, the following solutions can be used to implement 100G: > > > > >> 1、Combines four 25G lanes > > > > >> 2、Combines two 50G lanes > > > > >> 3、A single 100G lane > > > > >> > > > > >> It is assumed that two ports are interconnected and the two ports > > > > >> support > > > > >> the foregoing three solutions. But, we just configured the speed to > > > > >> 100G and > > > > >> one port uses four 25G lanes by default and the other port uses two > > > > >> 50G lanes > > > > >> by default, the port cannot be up. In this case, we need to > > > > >> configure the > > > > >> two ports to use the same solutions (for example, uses two 50G lanes) > > > > >> so that the ports can be up. > > > > > > > > > > Why this config is not OK? How do we know? > > > > > Really I have a very bad feeling about this feature. > > > > > > > > > > > > > > Sorry, I don't quite understand your question. > > > > Are you asking why cannot be up when one port uses four 25G lanes and > > > > the other port uses two 50G lanes? > > > > > > > > 100GBASE-SR2 (two 50G lanes) and 100GBASE-SR4 (four 25G lanes) have > > > > different standards at the physical layer.[1] > > > > So it's not possible to communicate. Configuring lanes can help the > > > > driver choose the same standard. > > > > > > Typically, low-level drivers like FW configure this. > > > > > > 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? > Having said that, If other NICs support this feature without > disturbing current port states, I don't have an objection to this API.
