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.
ethtool has supported lanes configuration a while ago.[1]
[1]
https://lore.kernel.org/netdev/20201010154119.3537085-1-ido...@idosch.org/T/
