When updating to Ethernet 1000BASE-X PCS/PMA or SGMII v14.3 released in Vivado 2014.3, intermittent link up failures are seen out of reset when targeting 7 Series GTX/GTH transceivers.
This failure was introduced in the v14.3 release in 2014.3 and is fixed in the v14.3 (Rev. 1) release in 2014.4.
To work around the failure in the v14.3 core in Vivado 2014.3, lock the core and make the following changes:
For information on locking the core so that the changes are not over-written, see (Xilinx Answer 57546).