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#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 */
};
A firmware (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 firmware_register the same name as the image).
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() 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.
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.
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.
Various system scripts and makefiles let you build a module by simply writing a Makefile with the following entries:
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.KMOD= imagename FIRMWS= image_file:imagename[:version] .include <bsd.kmod.mk>
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.
| FIRMWARE (9) | January 27, 2021 |
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