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 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 172endif # FW_LOADER 173endmenu 174
