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 <opendmb@gmail.com>]

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