PCIe Lane flip and PN flip (Lane reverse and polarity)

For the convenience of wiring, PCIE supports lane rollover and PN rollover, but the following principles must be followed:
1. PN rollover has no restrictions, it can roll over part of lane, or only TX or RX
. PN rollover is the characteristic of the receiving end, which will perform PN rollover on the received data after detecting PN rollover.
Polarity inversion is a function of the receiver and not the transmitter. The trans-mitter never inverts its data. During link training, the receiver examines symbols 6 through 15 of the TS1 and TS2 ordered sets for inversion of the PExRP[n] and PExRN[n] signals. If an inversion is detected, then logic for the receiving lane automatically inverts received data. Polarity inversion is a lane function and not a link function. Therefore, it is possible for some lanes of link to be inverted and for others not to be
2, turn lane must turn over all, Part can’t flip
3, lane to flip the TX/RX must turn at the same time, You cannot just flip TX or RX
4, lane flip and PN flip can exist at the same time

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