firmware_get(9) firmware image loading and management

Other Alias

firmware_register, firmware_unregister, firmware_put


In sys/param.h In sys/systm.h In sys/linker.h In sys/firmware.h

struct firmware {
const char *name; /* system-wide name */
const void *data; /* location of image */
size_t datasize; /* size of image in bytes */
unsigned int version; /* version of the image */

Ft const struct firmware * Fo firmware_register Fa const char *imagename Fa const void *data Fa size_t datasize Fa unsigned int version Fa const struct firmware *parent Fc Ft int Fn firmware_unregister const char *imagename Ft const struct firmware * Fn firmware_get const char *imagename Ft void Fn firmware_put const struct firmware *fp int flags


The firmware abstraction provides a convenient interface for loading firmware images into the kernel, and for accessing such images from kernel components.

A firmware image (or image for brevity) is an opaque block of data residing in kernel memory. It is associated to a unique imagename which constitutes a search key, and to an integer version number, which is also an opaque piece of information for the firmware subsystem.

An image is registered with the firmware subsystem by calling the function Fn firmware_register , and unregistered by calling Fn firmware_unregister . These functions are usually (but not exclusively) called by specially crafted kernel modules that contain the firmware image. The modules can be statically compiled in the kernel, or loaded by /boot/loader manually at runtime, or on demand by the firmware subsystem.

Clients of the firmware subsystem can request access to a given image by calling the function Fn firmware_get with the imagename they want as an argument. If a matching image is not already registered, the firmware subsystem will try to load it using the mechanisms specified below (typically, a kernel module with the same name as the image).


The kernel firmware API is made of the following functions:

Fn firmware_register registers with the kernel an image of size datasize located at address data under the name imagename

The function returns NULL on error (e.g. because an image with the same name already exists, or the image table is full), or a Ft const struct firmware * pointer to the image requested.

Fn firmware_unregister tries to unregister the firmware image imagename from the system. The function is successful and returns 0 if there are no pending references to the image, otherwise it does not unregister the image and returns EBUSY.

Fn firmware_get returns the requested firmware image. If the image is not yet registered with the system, the function tries to load it. This involves the linker subsystem and disk access, so Fn firmware_get must not be called with any locks (except for Giant ) Note also that if the firmware image is loaded from a filesystem it must already be mounted. In particular this means that it may be necessary to defer requests from a driver attach method unless it is known the root filesystem is already mounted.

On success, Fn firmware_get returns a pointer to the image description and increases the reference count for this image. On failure, the function returns NULL.

Fn firmware_put drops a reference to a firmware image. The Fa flags argument may be set to FIRMWARE_UNLOAD to indicate that firmware_put is free to reclaim resources associated with the firmware image if this is the last reference. By default a firmware image will be deferred to a taskqueue(9) thread so the call may be done while holding a lock. In certain cases, such as on driver detach, this cannot be allowed.


As mentioned before, any component of the system can register firmware images at any time by simply calling Fn firmware_register .

This is typically done when a module containing a firmware image is given control, whether compiled in, or preloaded by /boot/loader or manually loaded with kldload(8). However, a system can implement additional mechanisms to bring these images in memory before calling Fn firmware_register .

When Fn firmware_get does not find the requested image, it tries to load it using one of the available loading mechanisms. At the moment, there is only one, namely Loadable kernel modules

A firmware image named foo is looked up by trying to load the module named foo.ko using the facilities described in kld(4). In particular, images are looked up in the directories specified by the sysctl variable kern.module_path which on most systems defaults to /boot/kernel;/boot/modules

Note that in case a module contains multiple images, the caller should first request a Fn firmware_get for the first image contained in the module, followed by requests for the other images.


A firmware module is built by embedding the firmware image into a suitable loadable kernel module that calls Fn firmware_register on loading, and Fn firmware_unregister on unloading.

Various system scripts and makefiles let you build a module by simply writing a Makefile with the following entries:

        KMOD=   imagename
        FIRMWS= image_file:imagename[:version]
        .include <>
where KMOD is the basename of the module; FIRMWS is a list of colon-separated tuples indicating the image_file's to be embedded in the module, the imagename and version of each firmware image.

If you need to embed firmware images into a system, you should write appropriate entries in the <files.arch> file, e.g. this example is from sys/arm/xscale/ixp425/files.ixp425

ixp425_npe_fw.c                         optional npe_fw                 \
        compile-with    "${AWK} -f $S/tools/fw_stub.awk                 \
                        IxNpeMicrocode.dat:npe_fw -mnpe -c${.TARGET}"   \
        no-implicit-rule before-depend local                            \
        clean           "ixp425_npe_fw.c"
# NB: ld encodes the path in the binary symbols generated for the
#     firmware image so link the file to the object directory to
#     get known values for reference in the _fw.c file.
IxNpeMicrocode.fwo  optional npe_fw                                     \
        dependency      "IxNpeMicrocode.dat"                            \
        compile-with    "${LD} -b binary -d -warn-common                \
                            -r -d -o ${.TARGET} IxNpeMicrocode.dat"     \
        no-implicit-rule                                                \
        clean           "IxNpeMicrocode.fwo"
IxNpeMicrocode.dat                      optional npe_fw                 \
        dependency      ".PHONY"                                        \
        compile-with    "uudecode < $S/contrib/dev/npe/IxNpeMicrocode.dat.uu" \
        no-obj no-implicit-rule                                         \
        clean           "IxNpeMicrocode.dat"

Note that generating the firmware modules in this way requires the availability of the following tools: awk(1), make(1), the compiler and the linker.


The firmware system was introduced in Fx 6.1 .


This manual page was written by An Max Laier Aq [email protected] .