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: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/Documentation/firmware_class/README b/Documentation/firmware_class/README
index 7eceaff..815b711 100644
--- a/Documentation/firmware_class/README
+++ b/Documentation/firmware_class/README
@@ -18,32 +18,40 @@
High level behavior (mixed):
============================
- kernel(driver): calls request_firmware(&fw_entry, $FIRMWARE, device)
+ 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)
- userspace:
+ 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):