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 2/21/2023 11:53 AM, Doug Berger wrote:
> On 2/21/2023 11:41 AM, Andrew Lunn wrote:
> > On Tue, Feb 21, 2023 at 10:44:44AM -0800, Doug Berger wrote:
> > > 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.
> >
> > Are you talking about ethtool -s 
> > [master-slave|preferred-master|preferred-slave|forced-master|forced-slave]
> I am, though I was not aware of their addition to ethtool and I avoided 
> referencing them by name out of an overabundance of political 
> correctness ;).
>
> Thanks for bringing this to my attention.
>
> > The broadcom PHYs call genphy_config_aneg() -> __genphy_config_aneg()
> > -> genphy_setup_master_slave() which should configure this, even when
> > auto-neg is off.
> Yes, this sounds good. Perhaps Xiaolei is not setting these properly 
> when forcing 1000.
Hmmm. I just revisited 802.3-2018 40.5.2 MASTER-SLAVE configuration 
resolution and I see it contains this statement:
The MASTER-SLAVE relationship shall be determined
during Auto-Negotiation using Table 40–5 with the 1000BASE-T Technology 
Ability Next Page bit
values specified in Table 40–4 and information received from the link 
partner.

So it appears that the only normative behavior requires Auto-Negotiation 
to be enabled. It seems reasonable that an implementation might allow 
the forced-master and forced-slave configurations to be applied when 
Auto-Negotiation is not enabled, but this case is outside of the 
standard so an implementation could also fail to establish a link.

> >      Andrew
> Thanks again!
>      Doug