firmware: Add CONFIG_EXTRA_FIRMWARE option

This allows arbitrary firmware files to be included in the static kernel
where the firmware loader can find them without requiring userspace to
be alive.

(Updated and CONFIG_EXTRA_FIRMWARE_DIR added with lots of help from
Johannes Berg).

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

1 files changed, 39 insertions, 0 deletions

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index d7da109c24f..13cfcb435f7 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -34,6 +34,45 @@ config FW_LOADER
           require userspace firmware loading support, but a module built outside
           the kernel tree does.
 
+config EXTRA_FIRMWARE
+        string "External firmware blobs to build into the kernel binary"
+        depends on FW_LOADER
+        help
+          This option allows firmware to be built into the kernel, for the
+          cases where the user either cannot or doesn't want to provide it from
+          userspace at runtime (for example, when the firmware in question is
+          required for accessing the boot device, and the user doesn't want to
+          use an initrd).
+
+          This option is a string, and takes the (space-separated) names of the
+          firmware files -- the same names which appear in MODULE_FIRMWARE()
+          and request_firmware() in the source. These files should exist under
+          the directory specified by the EXTRA_FIRMWARE_DIR option, which is
+          by default the firmware/ subdirectory of the kernel source tree.
+
+          So, for example, you might set CONFIG_EXTRA_FIRMWARE="usb8388.bin",
+          copy the usb8388.bin file into the firmware/ directory, and build the
+          kernel. Then any request_firmware("usb8388.bin") will be
+          satisfied internally without needing to call out to userspace.
+
+          WARNING: If you include additional firmware files into your binary
+          kernel image which are not available under the terms of the GPL,
+          then it may be a violation of the GPL to distribute the resulting
+          image -- since it combines both GPL and non-GPL work. You should
+          consult a lawyer of your own before distributing such an image.
+
+config EXTRA_FIRMWARE_DIR
+        string "Firmware blobs root directory"
+        depends on EXTRA_FIRMWARE != ""
+        default "firmware"
+        help
+          This option controls the directory in which the kernel build system
+          looks for the firmware files listed in the EXTRA_FIRMWARE option.
+          The default is the firmware/ directory in the kernel source tree,
+          but by changing this option you can point it elsewhere, such as
+          the /lib/firmware/ directory or another separate directory
+          containing firmware files.
+
 config DEBUG_DRIVER
         bool "Driver Core verbose debug messages"
         depends on DEBUG_KERNEL