Hello NXP team,
we have custom T1042 board with SGMII connected to FPGA (SGMII core + MAC inside).
If autoneg is selected on FPGA side link fail to establish, if link is forced up on FPGA side it's possible to transmit data however frames pass only in T1042->FPGA direction, no frame can be received by T1042.
We've verified signals at physical layer - signals are of reference quality, no signal integrity issues.
From Linux side everything looks fine, link is described as "fixed" in device tree and ethtool report it up.
FPGA was tested by enabling loopback in FPGA's SedDes - link is up and MAC successfully receive own transmitted frames.
Honestly we have now idea how to debug this problem, maybe access to internal PSCPMA phy may help however standard Linux drivers do not expose it.