FIRMWARE(9) BSD Kernel Developer's Manual FIRMWARE(9)NAME
firmware_register, firmware_unregister, firmware_get, firmware_put —
firmware image loading and management
SYNOPSIS
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/linker.h>
#include <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 */
};
const struct firmware *
firmware_register(const char *imagename, const void *data,
size_t datasize, unsigned int version,
const struct firmware *parent);
int
firmware_unregister(const char *imagename);
const struct firmware *
firmware_get(const char *imagename);
void
firmware_put(const struct firmware *fp, int flags);
DESCRIPTION
The firmware abstraction provides a convenient interface for loading
firmware images into the kernel, and for accessing such images from ker‐
nel components.
A firmware image (or image for brevity) is an opaque block of data resid‐
ing in kernel memory. It is associated to a unique imagename which con‐
stitutes 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 func‐
tion firmware_register(), and unregistered by calling
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 sub‐
system.
Clients of the firmware subsystem can request access to a given image by
calling the function 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 (typi‐
cally, a kernel module with the same name as the image).
API DESCRIPTION
The kernel firmware API is made of the following functions:
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 const struct
firmware * pointer to the image requested.
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.
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 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, firmware_get() returns a pointer to the image description and
increases the reference count for this image. On failure, the function
returns NULL.
firmware_put() drops a reference to a firmware image. The 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.
FIRMWARE LOADING MECHANISMS
As mentioned before, any component of the system can register firmware
images at any time by simply calling 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 mech‐
anisms to bring these images in memory before calling
firmware_register().
When 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 firmware_get() for the first image contained in the mod‐
ule, followed by requests for the other images.
BUILDING FIRMWARE LOADABLE MODULES
A firmware module is built by embedding the firmware image into a suit‐
able loadable kernel module that calls firmware_register() on loading,
and 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 <bsd.kmod.mk>
where KMOD is the basename of the module; FIRMWS is a list of colon-sepa‐
rated 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 avail‐
ability of the following tools: awk(1), make(1), the compiler and the
linker.
SEE ALSOkld(4), module(9)
/usr/share/examples/kld/firmware
HISTORY
The firmware system was introduced in FreeBSD 6.1.
AUTHORS
This manual page was written by Max Laier ⟨mlaier@FreeBSD.org⟩.
BSD April 14, 2010 BSD
