Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
1# SPDX-License-Identifier: GPL-2.0
2menu "Firmware loader"
3
4config FW_LOADER
5 tristate "Firmware loading facility" if EXPERT
6 default y
7 help
8 This enables the firmware loading facility in the kernel. The kernel
9 will first look for built-in firmware, if it has any. Next, it will
10 look for the requested firmware in a series of filesystem paths:
11
12 o firmware_class path module parameter or kernel boot param
13 o /lib/firmware/updates/UTS_RELEASE
14 o /lib/firmware/updates
15 o /lib/firmware/UTS_RELEASE
16 o /lib/firmware
17
18 Enabling this feature only increases your kernel image by about
19 828 bytes, enable this option unless you are certain you don't
20 need firmware.
21
22 You typically want this built-in (=y) but you can also enable this
23 as a module, in which case the firmware_class module will be built.
24 You also want to be sure to enable this built-in if you are going to
25 enable built-in firmware (CONFIG_EXTRA_FIRMWARE).
26
27if FW_LOADER
28
29config EXTRA_FIRMWARE
30 string "Build named firmware blobs into the kernel binary"
31 help
32 Device drivers which require firmware can typically deal with
33 having the kernel load firmware from the various supported
34 /lib/firmware/ paths. This option enables you to build into the
35 kernel firmware files. Built-in firmware searches are preceded
36 over firmware lookups using your filesystem over the supported
37 /lib/firmware paths documented on CONFIG_FW_LOADER.
38
39 This may be useful for testing or if the firmware is required early on
40 in boot and cannot rely on the firmware being placed in an initrd or
41 initramfs.
42
43 This option is a string and takes the (space-separated) names of the
44 firmware files -- the same names that appear in MODULE_FIRMWARE()
45 and request_firmware() in the source. These files should exist under
46 the directory specified by the EXTRA_FIRMWARE_DIR option, which is
47 /lib/firmware by default.
48
49 For example, you might set CONFIG_EXTRA_FIRMWARE="usb8388.bin", copy
50 the usb8388.bin file into /lib/firmware, and build the kernel. Then
51 any request_firmware("usb8388.bin") will be satisfied internally
52 inside the kernel without ever looking at your filesystem at runtime.
53
54 WARNING: If you include additional firmware files into your binary
55 kernel image that are not available under the terms of the GPL,
56 then it may be a violation of the GPL to distribute the resulting
57 image since it combines both GPL and non-GPL work. You should
58 consult a lawyer of your own before distributing such an image.
59
60config EXTRA_FIRMWARE_DIR
61 string "Firmware blobs root directory"
62 depends on EXTRA_FIRMWARE != ""
63 default "/lib/firmware"
64 help
65 This option controls the directory in which the kernel build system
66 looks for the firmware files listed in the EXTRA_FIRMWARE option.
67
68config FW_LOADER_USER_HELPER
69 bool "Enable the firmware sysfs fallback mechanism"
70 help
71 This option enables a sysfs loading facility to enable firmware
72 loading to the kernel through userspace as a fallback mechanism
73 if and only if the kernel's direct filesystem lookup for the
74 firmware failed using the different /lib/firmware/ paths, or the
75 path specified in the firmware_class path module parameter, or the
76 firmware_class path kernel boot parameter if the firmware_class is
77 built-in. For details on how to work with the sysfs fallback mechanism
78 refer to Documentation/driver-api/firmware/fallback-mechanisms.rst.
79
80 The direct filesystem lookup for firmware is always used first now.
81
82 If the kernel's direct filesystem lookup for firmware fails to find
83 the requested firmware a sysfs fallback loading facility is made
84 available and userspace is informed about this through uevents.
85 The uevent can be suppressed if the driver explicitly requested it,
86 this is known as the driver using the custom fallback mechanism.
87 If the custom fallback mechanism is used userspace must always
88 acknowledge failure to find firmware as the timeout for the fallback
89 mechanism is disabled, and failed requests will linger forever.
90
91 This used to be the default firmware loading facility, and udev used
92 to listen for uvents to load firmware for the kernel. The firmware
93 loading facility functionality in udev has been removed, as such it
94 can no longer be relied upon as a fallback mechanism. Linux no longer
95 relies on or uses a fallback mechanism in userspace. If you need to
96 rely on one refer to the permissively licensed firmwared:
97
98 https://github.com/teg/firmwared
99
100 Since this was the default firmware loading facility at one point,
101 old userspace may exist which relies upon it, and as such this
102 mechanism can never be removed from the kernel.
103
104 You should only enable this functionality if you are certain you
105 require a fallback mechanism and have a userspace mechanism ready to
106 load firmware in case it is not found. One main reason for this may
107 be if you have drivers which require firmware built-in and for
108 whatever reason cannot place the required firmware in initramfs.
109 Another reason kernels may have this feature enabled is to support a
110 driver which explicitly relies on this fallback mechanism. Only two
111 drivers need this today:
112
113 o CONFIG_LEDS_LP55XX_COMMON
114 o CONFIG_DELL_RBU
115
116 Outside of supporting the above drivers, another reason for needing
117 this may be that your firmware resides outside of the paths the kernel
118 looks for and cannot possibly be specified using the firmware_class
119 path module parameter or kernel firmware_class path boot parameter
120 if firmware_class is built-in.
121
122 A modern use case may be to temporarily mount a custom partition
123 during provisioning which is only accessible to userspace, and then
124 to use it to look for and fetch the required firmware. Such type of
125 driver functionality may not even ever be desirable upstream by
126 vendors, and as such is only required to be supported as an interface
127 for provisioning. Since udev's firmware loading facility has been
128 removed you can use firmwared or a fork of it to customize how you
129 want to load firmware based on uevents issued.
130
131 Enabling this option will increase your kernel image size by about
132 13436 bytes.
133
134 If you are unsure about this, say N here, unless you are Linux
135 distribution and need to support the above two drivers, or you are
136 certain you need to support some really custom firmware loading
137 facility in userspace.
138
139config FW_LOADER_USER_HELPER_FALLBACK
140 bool "Force the firmware sysfs fallback mechanism when possible"
141 depends on FW_LOADER_USER_HELPER
142 help
143 Enabling this option forces a sysfs userspace fallback mechanism
144 to be used for all firmware requests which explicitly do not disable a
145 a fallback mechanism. Firmware calls which do prohibit a fallback
146 mechanism is request_firmware_direct(). This option is kept for
147 backward compatibility purposes given this precise mechanism can also
148 be enabled by setting the proc sysctl value to true:
149
150 /proc/sys/kernel/firmware_config/force_sysfs_fallback
151
152 If you are unsure about this, say N here.
153
154endif # FW_LOADER
155endmenu