phy: fixed link 1000 or 100 set with autoneg off

[Jia, Fang]

Hi Experts,

We use NXP LS1046 board and face an issue about the eth interface speed.

1) Scenario

we set fixed link 1000Mb/s in device tree.

However, after we set the auto-neg off, then the eth1's speed changed to 
10M and Duplex changed to Half.
The value of /sys/class/net/eth1/speed is 10 and 
/sys/class/net/eth1/duplex is half

2) Log is as following.

# ifconfig eth1 up
# ethtool eth1
Settings for eth1:
        Supported ports: [ MII ] 

        Supported link modes:   1000baseT/Full
        Supported pause frame use: Symmetric Receive-only
        Supports auto-negotiation: Yes 


        Supported FEC modes: Not reported 


        Advertised link modes:  1000baseT/Full
        Advertised pause frame use: Symmetric Receive-only 


        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Speed: 1000Mb/s
        Duplex: Full
        Port: MII
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: d
        Wake-on: d
        Current message level: 0xffffffff (-1)
                               drv probe link timer ifdown ifup rx_err 
tx_err tx_queued intr tx_done rx_status pktdata hw wol 0xffff8000
        Link detected: yes

# ethtool -s eth1 autoneg off
# ethtool eth1
Settings for eth1:
        Supported ports: [ MII ]
        Supported link modes:   1000baseT/Full
        Supported pause frame use: Symmetric Receive-only
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  1000baseT/Full
        Advertised pause frame use: Symmetric Receive-only
        Advertised auto-negotiation: No
        Advertised FEC modes: Not reported
        Speed: 10Mb/s
        Duplex: Half
        Port: MII
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: off
        Supports Wake-on: d
        Wake-on: d
        Current message level: 0xffffffff (-1)
                               drv probe link timer ifdown ifup rx_err 
tx_err tx_queued intr tx_done rx_status pktdata hw wol 0xffff8000
        Link detected: yes

3) After code tracing, we found that:

phy_state_machine()
	state PHY_RUNNING: phy_check_link_status()
		phy_read_status()
			genphy_read_status()
				genphy_read_status_fixed()

In genphy_read_status_fixed(), the speed and duplex changed.
It seems like the bmcr value is always 0x1000 from swphy_read_reg().

After revert the commit 726097d6d6d(net: phy: improve auto-neg emulation 
in swphy), then the Speed and Duplex shown comes back to 1000M and Full.

Could you please take a look it ? Can we revert this commit, is there 
any side impact ?

Best Regards,
Fang