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