Details:

VBUSM target interface in the PCIe subsytem may lock up if the following sequence of events happen:

1. Non-posted TLP is sent on the VBUSM target interface to PCIe subsystem.
2. This TLP request is initiated on the PCIe link. The PCIe logic unexpectedly receives linkdown event (link enters recovery) in the same core clock cycle as it initiates non-posted TLP to the PCIe link.
3. New request after linkdown reset handling is also a non-posted request.

When this sequence happens, the PCIe logic registers incorrect tag for the new request. When completion for the new request comes back, it is checked with respect to this incorrect tag and hence completion will not be accepted. PCIe logic will keep indefinitely waiting for completion with this incorrect tag. This leads to a lock up and VBUSM interface read command will never complete.

Probability of occurrence for this lock up is low because this requires link down event to propagate through internal logic and be captured during the same clock cycle as non-posted transaction is initiated.

Workaround(s):

None