[question] net: phy: rtl8211f: link speed shows 1000Mb/s but actual link speed in phy is 100Mb/s

From: Yonglong Liu
Date: Tue May 12 2020 - 08:48:29 EST


I use two devices, both support 1000M speed, they are directly connected
with a network cable. Two devices enable autoneg, and then do the following
test repeatedly:
ifconfig eth5 down
ifconfig eth5 up
sleep $((RANDOM%6))
ifconfig eth5 down
ifconfig eth5 up
sleep 10

With low probability, one device A link up with 100Mb/s, the other B link up with
1000Mb/s(the actual link speed read from phy is 100Mb/s), and the network can
not work.

device A:
Settings for eth5:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supported pause frame use: Symmetric Receive-only
Supports auto-negotiation: Yes
Supported FEC modes: Not reported
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Advertised pause frame use: Symmetric
Advertised auto-negotiation: Yes
Advertised FEC modes: Not reported
Link partner advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Link partner advertised pause frame use: Symmetric
Link partner advertised auto-negotiation: Yes
Link partner advertised FEC modes: Not reported
Speed: 100Mb/s
Duplex: Full
Port: MII
PHYAD: 3
Transceiver: internal
Auto-negotiation: on
Current message level: 0x00000036 (54)
probe link ifdown ifup
Link detected: yes

The regs value read from mdio are:
reg 9 = 0x200
reg a = 0

device B:
Settings for eth5:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supported pause frame use: Symmetric Receive-only
Supports auto-negotiation: Yes
Supported FEC modes: Not reported
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Advertised pause frame use: Symmetric
Advertised auto-negotiation: Yes
Advertised FEC modes: Not reported
Link partner advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Link partner advertised pause frame use: Symmetric
Link partner advertised auto-negotiation: Yes
Link partner advertised FEC modes: Not reported
Speed: 1000Mb/s
Duplex: Full
Port: MII
PHYAD: 3
Transceiver: internal
Auto-negotiation: on
Current message level: 0x00000036 (54)
probe link ifdown ifup
Link detected: yes

The regs value read from mdio are:
reg 9 = 0
reg a = 0x800

I had talk to the FAE of rtl8211f, they said if negotiation failed with 1000Mb/s,
rtl8211f will change reg 9 to 0, than try to negotiation with 100Mb/s.

The problem happened as:
ifconfig eth5 up -> phy_start -> phy_start_aneg -> phy_modify_changed(MII_CTRL1000)
(this time both A and B, reg 9 = 0x200) -> wait for link up -> (B: reg 9 changed to 0)
-> link up.

I think this is the bug of the rtl8211f itself, any one have an idea to avoid this bug?

When link up, update phydev->advertising before notify the eth driver, is this method
suitable? (phydev->advertising is config from user, if user just set one speed 1000M,
it's hard to )