oracular (9) firmware.9freebsd.gz

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 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.  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 firmware_register the same name as the image).

API DESCRIPTION

     The kernel firmware_register 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
     mechanisms 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 module, followed by requests for the other images.

BUILDING FIRMWARE LOADABLE MODULES

     A firmware module is built by embedding the firmware image into a suitable 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-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.

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>.