"The changes to the handling of the suspend and resume modes, mentioned by Torvalds and mainly developed by Rafael J. Wysocki, weren't integrated in one go, but found their way into the kernel (1, 2) gradually via the maintainers of the ACPI and PCI subsystems. Most of the relevant commits are comparatively small and seem rather inconspicuous at first glance (for example 1, 2, 3, 4).
"These changes, which have been in preparation for a long time, are to allow the kernel to reliably re-initialise the system's PCI(e) hardware when waking up from suspend mode. According to Torvalds, suspend and resume have worked on many systems, but haven't always been reliable due to interrupt timings, especially with shared interrupts ("We have historically been in a situation where suspend/resume often works, but may not be reliable due to interrupt timings, especially if there are any shared interrupts going on between drivers."). As these difficulties now seem resolved, Torvalds has called on users to report drivers that cause problems with suspend/resume."
