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 156