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+==============
+Firmware cache
+==============
+
+When Linux resumes from suspend some device drivers require firmware lookups to
+re-initialize devices. During resume there may be a period of time during which
+firmware lookups are not possible, during this short period of time firmware
+requests will fail. Time is of essence though, and delaying drivers to wait for
+the root filesystem for firmware delays user experience with device
+functionality. In order to support these requirements the firmware
+infrastructure implements a firmware cache for device drivers for most API
+calls, automatically behind the scenes.
+
+The firmware cache makes using certain firmware API calls safe during a device
+driver's suspend and resume callback. Users of these API calls needn't cache
+the firmware by themselves for dealing with firmware loss during system resume.
+
+The firmware cache works by requesting for firmware prior to suspend and
+caching it in memory. Upon resume device drivers using the firmware API will
+have access to the firmware immediately, without having to wait for the root
+filesystem to mount or dealing with possible race issues with lookups as the
+root filesystem mounts.
+
+Some implementation details about the firmware cache setup:
+
+* The firmware cache is setup by adding a devres entry for each device that
+ uses all synchronous call except :c:func:`request_firmware_into_buf`.
+
+* If an asynchronous call is used the firmware cache is only set up for a
+ device if if the second argument (uevent) to request_firmware_nowait() is
+ true. When uevent is true it requests that a kobject uevent be sent to
+ userspace for the firmware request through the sysfs fallback mechanism
+ if the firmware file is not found.
+
+* If the firmware cache is determined to be needed as per the above two
+ criteria the firmware cache is setup by adding a devres entry for the
+ device making the firmware request.
+
+* The firmware devres entry is maintained throughout the lifetime of the
+ device. This means that even if you release_firmware() the firmware cache
+ will still be used on resume from suspend.
+
+* The timeout for the fallback mechanism is temporarily reduced to 10 seconds
+ as the firmware cache is set up during suspend, the timeout is set back to
+ the old value you had configured after the cache is set up.
+
+* Upon suspend any pending non-uevent firmware requests are killed to avoid
+ stalling the kernel, this is done with kill_requests_without_uevent(). Kernel
+ calls requiring the non-uevent therefore need to implement their own firmware
+ cache mechanism but must not use the firmware API on suspend.
+