Re: BCM54220: After the BCM54220 closes the auto-negotiation, the configuration forces the 1000M network port to be linked down all the time.

[Doug Berger]

On 2/17/2023 12:06 AM, Wang, Xiaolei wrote:
> hi
>
>      When I use the nxp-imx7 board, eth0 is connected to the PC, eth0 is turned off the auto-negotiation mode, and the configuration is forced to 10M, 100M, 1000M. When configured to force 1000M，
>      The link status of phy status reg(0x1) is always 0, and the chip of phy is BCM54220, but I did not find the relevant datasheet on BCM official website, does anyone have any suggestions or the datasheet of BCM54220?
>
> thanks
> xiaolei
It is my understanding that the 1000BASE-T PHY requires peers to take on 
asymmetric roles and that establishment of these roles requires 
negotiation which occurs during auto-negotiation. Some PHYs may allow 
manual programming of these roles, but it is not standardized and tools 
like ethtool do not support manual specification of such details.

Therefore manual configuration of a 1000BASE-T link cannot be assumed to 
work. If you want to "force" a gigabit link you should keep 
auto-negotiation on and only advertise support for the speed you want.


Regards,

    Doug