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FIRMWARE(9) FreeBSD Kernel Developer's Manual FIRMWARE(9)
NAME
firmware_register, firmware_unregister, firmware_get, firmware_get_flags,
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);
const struct firmware *
firmware_get_flags(const char *imagename, uint32_t flags);
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
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 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
subsystem.
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, or by calling firmware_get_flags() with the imagename and flags
they want as an arguments. 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
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() and firmware_get_flags() return the requested firmware
image. The flags argument may be set to FIRMWARE_GET_NOWARN to indicate
that errors on firmware load or registration should only be logged in
case of booverbose. If the image is not yet registered with the system,
the functions try to load it. This involves the linker subsystem and
disk access, so firmware_get() or firmware_get_flags() 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() and firmware_get_flags() return a pointer to
the image description and increase the reference count for this image.
On failure, the functions return 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
mechanisms to bring these images in memory before calling
firmware_register().
When firmware_get() or firmware_get_flags() 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() or firmware_get_flags() for the first
image contained in the module, followed by requests for the other images.
BUILDING FIRMWARE LOADABLE MODULES
A firmware module is built by embedding the firmware image into a
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-
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"
Firmware was previously committed to the source tree as uuencoded files,
but this is no longer required; the binary firmware file should be
committed to the tree as provided by the vendor.
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.
SEE ALSO
kld(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>.
FreeBSD 14.0-RELEASE-p11 January 27, 2021 FreeBSD 14.0-RELEASE-p11