Hello,
This may be an emphasis / de-emphasis problem, as the issue exists at the physical layer. Probing the TX lines between the Xavier and the PCIe switch results in an eye diagram that “jumps” two two distinct high and two distinct low levels instead of just one distinct high and low.
I just found this post where @Manikanta solved the issue: How to change to pcie de-emphasis - #3 by 417383384
I have not flashed the Xavier with the modification to pcie-tegra.c yet for testing. However, I am curious at this point the full range of deemphasis levels that are available for PCIE_CAP_COMPLIANCE_PRESET in the PCIE_X4_RC_PF0_PCIE_CAP_LINK_CONTROL2_LINK_STATUS2_REG_0 register. The TRM does not go into detail, but since PCIE_CAP_COMPLIANCE_PRESET has four bits (15:12), there could be additional settings beyond -6.0 dB (0000b) and -3.5 dB (0001b).
Is there a description available of the PCIE_CAP_COMPLIANCE_PRESET settings?
Thanks!
Ian