7126 - How to disable the PCIe link through PCI Express Capability?
The bit[4] of the Link Control Register can be use to disable the link.
Note that this should be directly written from the Root Port and not from the Endpoint (this is a reserved bit for Endpoint).
In this example: the setpci command on Linux is use to write to the PCI Express Capability of the Root Port.
Once Link Disable bit is written with '1', the link is immediately disabled as seen on the Endpoint where it cannot access the configuration space anymore.
Additionally, link-up status signals each show a value of '0' when traced through Reveal Analyzer.