firmware loader: document firmware cache mechanism

This patch documents the firmware cache mechanism so that
users of request_firmware() know that it can be called
safely inside device's suspend and resume callback, and
the device's firmware needn't be cached any more by individual
driver itself to deal with firmware loss during system resume.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 7888af7..d814603 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -988,6 +988,9 @@
  *      firmware image for this or any other device.
  *
  *	Caller must hold the reference count of @device.
+ *
+ *	The function can be called safely inside device's suspend and
+ *	resume callback.
  **/
 int
 request_firmware(const struct firmware **firmware_p, const char *name,