1
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 FW_LOADER_PAGED_BUF
30 bool
31
32config EXTRA_FIRMWARE
33 string "Build named firmware blobs into the kernel binary"
34 help
35 Device drivers which require firmware can typically deal with
36 having the kernel load firmware from the various supported
37 /lib/firmware/ paths. This option enables you to build into the
38 kernel firmware files. Built-in firmware searches are preceded
39 over firmware lookups using your filesystem over the supported
40 /lib/firmware paths documented on CONFIG_FW_LOADER.
41
42 This may be useful for testing or if the firmware is required early on
43 in boot and cannot rely on the firmware being placed in an initrd or
44 initramfs.
45
46 This option is a string and takes the (space-separated) names of the
47 firmware files -- the same names that appear in MODULE_FIRMWARE()
48 and request_firmware() in the source. These files should exist under
49 the directory specified by the EXTRA_FIRMWARE_DIR option, which is
50 /lib/firmware by default.
51
52 For example, you might set CONFIG_EXTRA_FIRMWARE="usb8388.bin", copy
53 the usb8388.bin file into /lib/firmware, and build the kernel. Then
54 any request_firmware("usb8388.bin") will be satisfied internally
55 inside the kernel without ever looking at your filesystem at runtime.
56
57 WARNING: If you include additional firmware files into your binary
58 kernel image that are not available under the terms of the GPL,
59 then it may be a violation of the GPL to distribute the resulting
60 image since it combines both GPL and non-GPL work. You should
61 consult a lawyer of your own before distributing such an image.
62
63config EXTRA_FIRMWARE_DIR
64 string "Firmware blobs root directory"
65 depends on EXTRA_FIRMWARE != ""
66 default "/lib/firmware"
67 help
68 This option controls the directory in which the kernel build system
69 looks for the firmware files listed in the EXTRA_FIRMWARE option.
70
71config FW_LOADER_USER_HELPER
72 bool "Enable the firmware sysfs fallback mechanism"
73 select FW_LOADER_PAGED_BUF
74 help
75 This option enables a sysfs loading facility to enable firmware
76 loading to the kernel through userspace as a fallback mechanism
77 if and only if the kernel's direct filesystem lookup for the
78 firmware failed using the different /lib/firmware/ paths, or the
79 path specified in the firmware_class path module parameter, or the
80 firmware_class path kernel boot parameter if the firmware_class is
81 built-in. For details on how to work with the sysfs fallback mechanism
82 refer to Documentation/driver-api/firmware/fallback-mechanisms.rst.
83
84 The direct filesystem lookup for firmware is always used first now.
85
86 If the kernel's direct filesystem lookup for firmware fails to find
87 the requested firmware a sysfs fallback loading facility is made
88 available and userspace is informed about this through uevents.
89 The uevent can be suppressed if the driver explicitly requested it,
90 this is known as the driver using the custom fallback mechanism.
91 If the custom fallback mechanism is used userspace must always
92 acknowledge failure to find firmware as the timeout for the fallback
93 mechanism is disabled, and failed requests will linger forever.
94
95 This used to be the default firmware loading facility, and udev used
96 to listen for uvents to load firmware for the kernel. The firmware
97 loading facility functionality in udev has been removed, as such it
98 can no longer be relied upon as a fallback mechanism. Linux no longer
99 relies on or uses a fallback mechanism in userspace. If you need to
100 rely on one refer to the permissively licensed firmwared:
101
102 https://github.com/teg/firmwared
103
104 Since this was the default firmware loading facility at one point,
105 old userspace may exist which relies upon it, and as such this
106 mechanism can never be removed from the kernel.
107
108 You should only enable this functionality if you are certain you
109 require a fallback mechanism and have a userspace mechanism ready to
110 load firmware in case it is not found. One main reason for this may
111 be if you have drivers which require firmware built-in and for
112 whatever reason cannot place the required firmware in initramfs.
113 Another reason kernels may have this feature enabled is to support a
114 driver which explicitly relies on this fallback mechanism. Only two
115 drivers need this today:
116
117 o CONFIG_LEDS_LP55XX_COMMON
118 o CONFIG_DELL_RBU
119
120 Outside of supporting the above drivers, another reason for needing
121 this may be that your firmware resides outside of the paths the kernel
122 looks for and cannot possibly be specified using the firmware_class
123 path module parameter or kernel firmware_class path boot parameter
124 if firmware_class is built-in.
125
126 A modern use case may be to temporarily mount a custom partition
127 during provisioning which is only accessible to userspace, and then
128 to use it to look for and fetch the required firmware. Such type of
129 driver functionality may not even ever be desirable upstream by
130 vendors, and as such is only required to be supported as an interface
131 for provisioning. Since udev's firmware loading facility has been
132 removed you can use firmwared or a fork of it to customize how you
133 want to load firmware based on uevents issued.
134
135 Enabling this option will increase your kernel image size by about
136 13436 bytes.
137
138 If you are unsure about this, say N here, unless you are Linux
139 distribution and need to support the above two drivers, or you are
140 certain you need to support some really custom firmware loading
141 facility in userspace.
142
143config FW_LOADER_USER_HELPER_FALLBACK
144 bool "Force the firmware sysfs fallback mechanism when possible"
145 depends on FW_LOADER_USER_HELPER
146 help
147 Enabling this option forces a sysfs userspace fallback mechanism
148 to be used for all firmware requests which explicitly do not disable a
149 a fallback mechanism. Firmware calls which do prohibit a fallback
150 mechanism is request_firmware_direct(). This option is kept for
151 backward compatibility purposes given this precise mechanism can also
152 be enabled by setting the proc sysctl value to true:
153
154 /proc/sys/kernel/firmware_config/force_sysfs_fallback
155
156 If you are unsure about this, say N here.
157
158config FW_LOADER_COMPRESS
159 bool "Enable compressed firmware support"
160 select FW_LOADER_PAGED_BUF
161 select XZ_DEC
162 help
163 This option enables the support for loading compressed firmware
164 files. The caller of firmware API receives the decompressed file
165 content. The compressed file is loaded as a fallback, only after
166 loading the raw file failed at first.
167
168 Currently only XZ-compressed files are supported, and they have to
169 be compressed with either none or crc32 integrity check type (pass
170 "-C crc32" option to xz command).
171
172config FW_CACHE
173 bool "Enable firmware caching during suspend"
174 depends on PM_SLEEP
175 default y if PM_SLEEP
176 help
177 Because firmware caching generates uevent messages that are sent
178 over a netlink socket, it can prevent suspend on many platforms.
179 It is also not always useful, so on such platforms we have the
180 option.
181
182 If unsure, say Y.
183
184endif
185endmenu
186
