Linux 7.4 improves hibernation power management for PCIe bridges

Improvements to the PCI/PCIe subsystem have been merged into the Linux 7.4 merge window. The update ensures that PCIe bridges with downstream devices are transitioned to low-power states during hibernation, a step previously missing from the hibernate poweroff flow.

Aligning hibernation with suspend behavior

• During S3 suspend, pci_pm_suspend_noirq() puts PCIe bridges with downstream devices into D3hot or D3cold states.
• Previously, the hibernate poweroff_noirq path only called pci_prepare_to_sleep() for devices without subordinates.
• This meant bridges with active children remained in D0 during hibernation.
• The fix allows bridges to power down during S4 hibernation, assisting hardware designs (especially those with dGPUs) in meeting energy certification criteria.

Why it matters

This change helps hardware manufacturers meet global energy efficiency standards for devices running Linux, particularly in systems with discrete GPUs.