net: phy: dp83867: retrigger SGMII AN when link change

commit c76acfb7 upstream.

There is a limitation in TI DP83867 PHY device where SGMII AN is only
triggered once after the device is booted up. Even after the PHY TPI is
down and up again, SGMII AN is not triggered and hence no new in-band
message from PHY to MAC side SGMII.

This could cause an issue during power up, when PHY is up prior to MAC.
At this condition, once MAC side SGMII is up, MAC side SGMII wouldn`t
receive new in-band message from TI PHY with correct link status, speed
and duplex info.

As suggested by TI, implemented a SW solution here to retrigger SGMII
Auto-Neg whenever there is a link change.

v2: Add Fixes tag in commit message.

Fixes: 2a10154a

 ("net: phy: dp83867: Add TI dp83867 phy")
Cc: <stable@vger.kernel.org> # 5.4.x
Signed-off-by: Sit, Michael Wei Hong <michael.wei.hong.sit@intel.com>
Reviewed-by: Voon Weifeng <weifeng.voon@intel.com>
Signed-off-by: Tan Tee Min <tee.min.tan@linux.intel.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220526090347.128742-1-tee.min.tan@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>