driver-api/firmware/firmware_cache.rst

5 When Linux resumes from suspend some device drivers require firmware lookups to
6 re-initialize devices. During resume there may be a period of time during which
8 requests will fail. Time is of essence though, and delaying drivers to wait for
10 functionality. In order to support these requirements the firmware
15 driver's suspend and resume callback.  Users of these API calls needn't cache
18 The firmware cache works by requesting for firmware prior to suspend and
19 caching it in memory. Upon resume device drivers using the firmware API will
20 have access to the firmware immediately, without having to wait for the root
41   will still be used on resume from suspend.
44   as the firmware cache is set up during suspend, the timeout is set back to
47 * Upon suspend any pending non-uevent firmware requests are killed to avoid
49   calls requiring the non-uevent therefore need to implement their own firmware
50   cache mechanism but must not use the firmware API on suspend.