PCI Changes For Linux 5.8 Bring Power Savings, AMD Workarounds/Whitelisting

Linux 5.8 has merged all of the PCI/PCIe subsystem updates and there are a number of notable changes.

PCI highlights for Linux 5.8 include:

- As previously reported, the possibility of "significant" power savings for systems with PCI Express to PCI or PCI-X bridges. Previously Active State Power Management (ASPM) wasn't being enabled for such bridges for unknown reasons. But in enabling it can yield big power advantages for server platforms and more having the PCIe to PCI/PCI-X bridges.

- The Linux kernel will now avoid doing function level resets (FLR) for AMD Starship with USB 3.0 and AMD Matisse with HD Audio and USB 3.0. While the Starship/Matisse chipsets advertise FLR support, making use of it can lead to system lockups. As such, at least until a proper workaround can be sorted out, FLR support is blocked for this AMD hardware.

- AMD Raven Ridge and Renoir root ports are now whitelisted for the peer-to-peer DMA support.

- Thunderbolt resume time has been reduced by working around devices not supporting DLL Link Active reporting.

- Various other PCI improvements and fixes.

The full list of Linux 5.8 PCI(e) work via this pull request.