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.
