"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."
