Linux 7.2 Fixes Where PCIe Devices Could Be Inadvertently Restricted To 2.5 GT/s

The PCI/PCIe subsystem changes have been merged this week as we approach the end of the Linux 7.2 merge window.

The PCI code has lifted a 2.5GT/s speed restriction in the PCIe failed-link retraining code to avoid a situation where a link could be restricted to 2.5GT/s after hot-plug changes to the PCIe device.

Maciej Rozycki explained of the possible 2.5GT/s restriction going awry in ths patch:

“Discard Vendor:Device ID matching in the PCIe failed link retraining quirk and ignore the link status for the removal of the 2.5GT/s speed clamp, whether applied by the quirk itself or the firmware earlier on.

Revert to the original target link speed if this final link retraining has failed.

This is so that link training noise in hot-plug scenarios does not make a link remain clamped to the 2.5GT/s speed where an event race has led the quirk to apply the speed clamp for one device, only to leave it in place for a subsequent device to be plugged in.”

This fixes problematic code introduced in the Linux kernel back in 2023 with this 2.5GT/s restriction trying to workaround PCIe link training failures at the time. This work is set to be back-ported to existing stable Linux kernel versions as well.

Separately, the Intel QAT, DSA, and IAA accelerator devices have been added to the peer-to-peer DMA (P2PDMA) whitelist.

A new PCI driver this cycle is the UltraRISC DP1000 PCIe controller. Much of the other PCI changes for Linux 7.2 include the usual driver maintenance and other routine fixes.

More details on these PCI changes for Linux 7.2 via this pull request.

Source