man/man9/firmware.9

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.Dd January 25, 2024
.Dt FIRMWARE 9
.Os
.Sh NAME
.Nm firmware_register ,
.Nm firmware_unregister ,
.Nm firmware_get ,
.Nm firmware_get_flags ,
.Nm firmware_put
.Nd firmware image loading and management
.Sh SYNOPSIS
.In sys/param.h
.In sys/systm.h
.In sys/linker.h
.In sys/firmware.h
.Bd -literal
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 */
};
.Ed
.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 "const struct firmware *"
.Fn firmware_get_flags "const char *imagename" "uint32_t flags"
.Ft void
.Fn firmware_put "const struct firmware *fp" "int flags"
.Sh DESCRIPTION
The
.Nm firmware
abstraction provides a convenient interface for loading
.Nm firmware images
into the kernel, and for accessing such images from kernel components.
.Pp
A
.Nm firmware image
(or
.Nm image
for brevity)
is an opaque block of data residing in kernel memory.
It is associated to a unique
.Nm imagename
which constitutes a search key, and to an integer
.Nm version
number, which is also an opaque piece of information for the
firmware subsystem.
.Pp
An image is registered with the
.Nm 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
.Pa /boot/loader ,
manually at runtime, or on demand by the firmware subsystem.
.Pp
Firmware binary files may also be loaded directly rather than embedded into
kernel modules.
.Pp
.Nm Clients
of the firmware subsystem can request access to a given image
by calling the function
.Fn firmware_get
with the
.Nm imagename
they want as an argument, or by calling
.Fn firmware_get_flags
with the
.Nm imagename
and
.Nm 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
.Nm
the same name
as the image).
.Sh API DESCRIPTION
The kernel
.Nm
firmware API
is made of the following functions:
.Pp
.Fn firmware_register
registers with the kernel an image of size
.Nm datasize
located at address
.Nm data ,
under the name
.Nm imagename .
.Pp
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.
.Pp
.Fn firmware_unregister
tries to unregister the firmware image
.Nm 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.
.Pp
.Fn firmware_get
and
.Fn firmware_get_flags
return the requested firmware image.
The
.Fa flags
argument may be set to
.Dv FIRMWARE_GET_NOWARN
to indicate that errors on firmware load or registration should
only be logged in case of
.Nm 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
.Fn firmware_get
or
.Fn firmware_get_flags
must not be called with any locks (except for
.Va 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.
.Pp
On success,
.Fn firmware_get
and
.Fn firmware_get_flags
return a pointer to the image description and increase the reference count
for this image.
On failure, the functions return NULL.
.Pp
.Fn firmware_put
drops a reference to a firmware image.
The
.Fa flags
argument may be set to
.Dv 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
.Xr 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.
.Sh FIRMWARE LOADING VIA MODULES
As mentioned before, any component of the system can register
firmware images at any time by simply calling
.Fn firmware_register .
.Pp
This is typically done when a module containing
a firmware image is given control,
whether compiled in, or preloaded by
.Pa /boot/loader ,
or manually loaded with
.Xr kldload 8 .
However, a system can implement additional mechanisms to bring
these images in memory before calling
.Fn firmware_register .
.Pp
When
.Fn firmware_get
or
.Fn 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
.Nm Loadable kernel modules .
.Pp
A firmware image named
.Nm foo
is looked up by trying to load the module named
.Nm foo.ko ,
using the facilities described in
.Xr kld 4 .
In particular, images are looked up in the directories specified
by the sysctl variable
.Nm kern.module_path
which on most systems defaults to
.Pa /boot/kernel;/boot/modules .
.Pp
Note that in case a module contains multiple images,
the caller should first request a
.Fn firmware_get
or
.Fn firmware_get_flags
for the first image contained in the module, followed by requests
for the other images.
.Sh BUILDING FIRMWARE LOADABLE MODULES
A firmware module is built by embedding the
.Nm firmware image
into a suitable loadable kernel module that calls
.Fn firmware_register
on loading, and
.Fn firmware_unregister
on unloading.
.Pp
Various system scripts and makefiles let you build a module
by simply writing a Makefile with the following entries:
.Bd -literal

        KMOD=   imagename
        FIRMWS= image_file:imagename[:version]
        .include <bsd.kmod.mk>

.Ed
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.
.Pp
If you need to embed firmware images into a system, you should write
appropriate entries in the <files.arch> or <files> file, e.g. this example is
from
.Nm sys/conf/files
.Bd -literal
iwn1000fw.c			optional iwn1000fw | iwnfw		\\
	compile-with	"${AWK} -f $S/tools/fw_stub.awk iwn1000.fw:iwn1000fw -miwn1000fw -c${.TARGET}" \\
	no-ctfconvert no-implicit-rule before-depend local		\\
	clean		"iwn1000fw.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.
#
iwn1000fw.fwo			optional iwn1000fw | iwnfw		\\
	dependency	"iwn1000.fw"					\\
	compile-with	"${NORMAL_FWO}"					\\
	no-implicit-rule						\\
	clean		"iwn1000fw.fwo"
.Ed
.Pp
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.
.Pp
Note that generating the firmware modules in this way requires
the availability of the following tools:
.Xr awk 1 ,
.Xr make 1 ,
the compiler and the linker.
.Sh LOADING BINARY FIRMWARE FILES
.Ss Binary Firmware Format
Binary firmware files can also be loaded, either from
.Pa /boot/loader ,
or when
.Nm firmware_get
cannot find the registered firmware from a kernel module.
Binary firmware files are raw binary files that the creator of the firmware
made.
They offer an easier way to load firmware, but one that lacks the full
flexibility and generality of kernel modules with the following restrictions:
.Bl -bullet -compact
.It
Binary firmware files only hold one set of firmware.
.It
They do not offer kernel module dependencies to ensure they are loaded
automatically by the boot loader.
.It
They cannot be compiled into the kernel.
.It
The
.Nm imagename
is identical to the full path name used to load the module.
.It
The version number is assumed to be zero.
.El
.Ss Loading from Pa /boot/loader
Binary firmware files may be loaded either from the command line with
.Dq load -t firmware /boot/firmware/filename
or using the
.Xr loader.conf 5
mechanism to load modules with a type of
.Dq firmware
For example
.Bd -literal
wififw_load="YES"
wififw_name="/boot/firmware/wifi2034_fw.bin"
wififw_type="firmware"
.Ed
.Ss On demand loading from Nm firmware_get
If no kernel module with an embedded firmware image named
.Nm imagename
is loaded, then
.Nm imagename
will be appended to the module path (by default
.Pa /boot/firmware/ )
and if that file exists, it will be loaded and registered using
.Nm firmware_register
using the full path to the filename as
.Nm imagename .
.Ss Searching for imagename
.Nm firmware_get
uses the following algorithm to find firmware images:
.Bl -bullet -compact
.It
If an existing firmware image is registered for
.Fa imagename,
that image is returned.
.It
If
.Fa imagename
matches the trailing subpath of a registered image with a full path, that image is returned.
.It
he kernel linker searches for a kernel module named
.Fa imagename .
If a kernel module is found, it is loaded, and
the list of registered firmware images is searched again.
If a match is found, the matching image is returned.
.It
The kernel searches for a file named
.Fa imagename
in the firmware image path
(by default
.Pa /boot/firmware/ ) .
If that file exists and can be read,
it contents are registered as a firmware image with the full path as the
.Nm imagename
and that firmware is returned.
Currently, there is an 8MB limit on the size of the firmware image.
This can be changed by by the sysctl variable
.Nm debug.max_firmware_size .
.El
.Sh SEE ALSO
.Xr kld 4 ,
.Xr module 9
.Pp
.Pa /boot/firmware
.Pp
.Pa /usr/share/examples/kld/firmware
.Sh HISTORY
The
.Nm firmware
system was introduced in
.Fx 6.1 .
Binary firmware loading was introduced in
.Fx 15.0 .
.Sh AUTHORS
This manual page was written by
.An Max Laier Aq Mt mlaier@FreeBSD.org .