6f65b50546
With the upcoming usage from LinuxKPI but also from drivers
ported natively we are seeing more probing of various
firmware (names).
Add the ability to firmware(9) to silence the
"firmware image loading/registering errors" by adding a new
firmware_get_flags() functions extending firmware_get() and
taking a flags argument as firmware_put() already does.
Requested-by: zeising (for future LinuxKPI/DRM)
Sponsored-by: The FreeBSD Foundation
Sponsored-by: Rubicon Communications, LLC ("Netgate")
MFC after: 3 days
Reviewed-by: markj
Differential Revision: https://reviews.freebsd.org/D27413
301 lines
9.1 KiB
Groff
301 lines
9.1 KiB
Groff
.\" Copyright (c) 2006 Max Laier <mlaier@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 27, 2021
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.Dt FIRMWARE 9
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.Os
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.Sh NAME
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.Nm firmware_register ,
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.Nm firmware_unregister ,
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.Nm firmware_get ,
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.Nm firmware_get_flags ,
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.Nm firmware_put
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.Nd firmware image loading and management
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/systm.h
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.In sys/linker.h
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.In sys/firmware.h
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.Bd -literal
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struct firmware {
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const char *name; /* system-wide name */
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const void *data; /* location of image */
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size_t datasize; /* size of image in bytes */
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unsigned int version; /* version of the image */
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};
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.Ed
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.Ft "const struct firmware *"
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.Fo firmware_register
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.Fa "const char *imagename"
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.Fa "const void *data"
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.Fa "size_t datasize"
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.Fa "unsigned int version"
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.Fa "const struct firmware *parent"
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.Fc
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.Ft int
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.Fn firmware_unregister "const char *imagename"
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.Ft "const struct firmware *"
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.Fn firmware_get "const char *imagename"
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.Ft "const struct firmware *"
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.Fn firmware_get_flags "const char *imagename" "uint32_t flags"
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.Ft void
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.Fn firmware_put "const struct firmware *fp" "int flags"
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.Sh DESCRIPTION
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The
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.Nm firmware
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abstraction provides a convenient interface for loading
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.Nm firmware images
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into the kernel, and for accessing such images from kernel components.
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.Pp
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A
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.Nm firmware image
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(or
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.Nm image
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for brevity)
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is an opaque block of data residing in kernel memory.
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It is associated to a unique
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.Nm imagename
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which constitutes a search key, and to an integer
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.Nm version
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number, which is also an opaque piece of information for the
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firmware subsystem.
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.Pp
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An image is registered with the
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.Nm firmware
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subsystem by calling the function
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.Fn firmware_register ,
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and unregistered by calling
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.Fn firmware_unregister .
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These functions are usually (but not exclusively) called by
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specially crafted kernel modules that contain the firmware image.
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The modules can be statically compiled in the kernel, or loaded by
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.Nm /boot/loader ,
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manually at runtime, or on demand by the firmware subsystem.
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.Pp
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.Nm Clients
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of the firmware subsystem can request access to a given image
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by calling the function
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.Fn firmware_get
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with the
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.Nm imagename
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they want as an argument, or by calling
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.Fn firmware_get_flags
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with the
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.Nm imagename
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and
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.Nm flags
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they want as an arguments.
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If a matching image is not already registered,
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the firmware subsystem will try to load it using the
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mechanisms specified below (typically, a kernel module
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with
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.Nm
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the same name
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as the image).
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.Sh API DESCRIPTION
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The kernel
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.Nm
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firmware API
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is made of the following functions:
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.Pp
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.Fn firmware_register
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registers with the kernel an image of size
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.Nm datasize
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located at address
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.Nm data ,
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under the name
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.Nm imagename .
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.Pp
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The function returns NULL on error (e.g. because an
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image with the same name already exists, or the image
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table is full), or a
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.Ft const struct firmware *
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pointer to the image requested.
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.Pp
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.Fn firmware_unregister
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tries to unregister the firmware image
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.Nm imagename
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from the system.
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The function is successful and returns 0
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if there are no pending references to the image, otherwise
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it does not unregister the image and returns EBUSY.
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.Pp
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.Fn firmware_get
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and
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.Fn firmware_get_flags
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return the requested firmware image.
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The
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.Fa flags
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argument may be set to
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.Dv FIRMWARE_GET_NOWARN
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to indicate that errors on firmware load or registration should
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only be logged in case of
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.Nm booverbose .
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If the image is not yet registered with the system,
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the functions try to load it.
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This involves the linker subsystem and disk access, so
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.Fn firmware_get
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or
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.Fn firmware_get_flags
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must not be called with any locks (except for
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.Va Giant ) .
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Note also that if the firmware image is loaded from a filesystem
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it must already be mounted.
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In particular this means that it may be necessary to defer requests
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from a driver attach method unless it is known the root filesystem is
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already mounted.
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.Pp
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On success,
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.Fn firmware_get
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and
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.Fn firmware_get_flags
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return a pointer to the image description and increase the reference count
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for this image.
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On failure, the functions return NULL.
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.Pp
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.Fn firmware_put
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drops a reference to a firmware image.
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The
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.Fa flags
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argument may be set to
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.Dv FIRMWARE_UNLOAD
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to indicate that
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firmware_put is free to reclaim resources associated with
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the firmware image if this is the last reference.
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By default a firmware image will be deferred to a
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.Xr taskqueue 9
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thread so the call may be done while holding a lock.
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In certain cases, such as on driver detach, this cannot be allowed.
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.Sh FIRMWARE LOADING MECHANISMS
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As mentioned before, any component of the system can register
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firmware images at any time by simply calling
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.Fn firmware_register .
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.Pp
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This is typically done when a module containing
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a firmware image is given control,
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whether compiled in, or preloaded by
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.Nm /boot/loader ,
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or manually loaded with
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.Xr kldload 8 .
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However, a system can implement additional mechanisms to bring
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these images in memory before calling
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.Fn firmware_register .
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.Pp
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When
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.Fn firmware_get
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or
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.Fn firmware_get_flags
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does not find the requested image, it tries to load it using
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one of the available loading mechanisms.
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At the moment, there is only one, namely
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.Nm Loadable kernel modules .
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.Pp
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A firmware image named
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.Nm foo
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is looked up by trying to load the module named
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.Nm foo.ko ,
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using the facilities described in
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.Xr kld 4 .
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In particular, images are looked up in the directories specified
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by the sysctl variable
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.Nm kern.module_path
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which on most systems defaults to
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.Nm /boot/kernel;/boot/modules .
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.Pp
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Note that in case a module contains multiple images,
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the caller should first request a
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.Fn firmware_get
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or
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.Fn firmware_get_flags
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for the first image contained in the module, followed by requests
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for the other images.
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.Sh BUILDING FIRMWARE LOADABLE MODULES
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A firmware module is built by embedding the
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.Nm firmware image
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into a suitable loadable kernel module that calls
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.Fn firmware_register
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on loading, and
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.Fn firmware_unregister
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on unloading.
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.Pp
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Various system scripts and makefiles let you build a module
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by simply writing a Makefile with the following entries:
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.Bd -literal
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KMOD= imagename
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FIRMWS= image_file:imagename[:version]
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.include <bsd.kmod.mk>
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.Ed
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where KMOD is the basename of the module; FIRMWS is a list of
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colon-separated tuples indicating the image_file's to be embedded
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in the module, the imagename and version of each firmware image.
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.Pp
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If you need to embed firmware images into a system, you should write
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appropriate entries in the <files.arch> file, e.g. this example is
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from
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.Nm sys/arm/xscale/ixp425/files.ixp425 :
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.Bd -literal
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ixp425_npe_fw.c optional npe_fw \\
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compile-with "${AWK} -f $S/tools/fw_stub.awk \\
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IxNpeMicrocode.dat:npe_fw -mnpe -c${.TARGET}" \\
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no-implicit-rule before-depend local \\
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clean "ixp425_npe_fw.c"
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#
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# NB: ld encodes the path in the binary symbols generated for the
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# firmware image so link the file to the object directory to
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# get known values for reference in the _fw.c file.
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#
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IxNpeMicrocode.fwo optional npe_fw \\
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dependency "IxNpeMicrocode.dat" \\
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compile-with "${LD} -b binary -d -warn-common \\
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-r -d -o ${.TARGET} IxNpeMicrocode.dat" \\
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no-implicit-rule \\
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clean "IxNpeMicrocode.fwo"
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.Ed
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.Pp
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Firmware was previously committed to the source tree as uuencoded files,
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but this is no longer required; the binary firmware file should be committed
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to the tree as provided by the vendor.
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.Pp
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Note that generating the firmware modules in this way requires
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the availability of the following tools:
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.Xr awk 1 ,
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.Xr make 1 ,
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the compiler and the linker.
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.Sh SEE ALSO
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.Xr kld 4 ,
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.Xr module 9
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.Pp
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.Pa /usr/share/examples/kld/firmware
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.Sh HISTORY
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The
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.Nm firmware
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system was introduced in
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.Fx 6.1 .
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.Sh AUTHORS
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This manual page was written by
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.An Max Laier Aq Mt mlaier@FreeBSD.org .
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