firmware loader: document kernel direct loading

This patch adds description on recently introduced direct firmware
loading by Linus.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/firmware_class/README

@@ -18,32 +18,40 @@
  High level behavior (mixed):
  ============================
 
- kernel(driver): calls request_firmware(&fw_entry, $FIRMWARE, device)
-
- userspace:
+ 1), kernel(driver):
+	- calls request_firmware(&fw_entry, $FIRMWARE, device)
+	- kernel searchs the fimware image with name $FIRMWARE directly
+	in the below search path of root filesystem:
+		"/lib/firmware/updates/" UTS_RELEASE,
+		"/lib/firmware/updates",
+		"/lib/firmware/" UTS_RELEASE,
+		"/lib/firmware"
+	- If found, goto 7), else goto 2)
+
+ 2), userspace:
  	- /sys/class/firmware/xxx/{loading,data} appear.
 	- hotplug gets called with a firmware identifier in $FIRMWARE
 	  and the usual hotplug environment.
 		- hotplug: echo 1 > /sys/class/firmware/xxx/loading
 
- kernel: Discard any previous partial load.
+ 3), kernel: Discard any previous partial load.
 
- userspace:
+ 4), userspace:
 		- hotplug: cat appropriate_firmware_image > \
 					/sys/class/firmware/xxx/data
 
- kernel: grows a buffer in PAGE_SIZE increments to hold the image as it
+ 5), kernel: grows a buffer in PAGE_SIZE increments to hold the image as it
 	 comes in.
 
- userspace:
+ 6), userspace:
 		- hotplug: echo 0 > /sys/class/firmware/xxx/loading
 
- kernel: request_firmware() returns and the driver has the firmware
+ 7), kernel: request_firmware() returns and the driver has the firmware
 	 image in fw_entry->{data,size}. If something went wrong
 	 request_firmware() returns non-zero and fw_entry is set to
 	 NULL.
 
- kernel(driver): Driver code calls release_firmware(fw_entry) releasing
+ 8), kernel(driver): Driver code calls release_firmware(fw_entry) releasing
 		 the firmware image and any related resource.
 
  High level behavior (driver code):