1================= 2Built-in firmware 3================= 4 5Firmware can be built-in to the kernel, this means building the firmware 6into vmlinux directly, to enable avoiding having to look for firmware from 7the filesystem. Instead, firmware can be looked for inside the kernel 8directly. You can enable built-in firmware using the kernel configuration 9options: 10 11 * CONFIG_EXTRA_FIRMWARE 12 * CONFIG_EXTRA_FIRMWARE_DIR 13 14This should not be confused with CONFIG_FIRMWARE_IN_KERNEL, this is for drivers 15which enables firmware to be built as part of the kernel build process. This 16option, CONFIG_FIRMWARE_IN_KERNEL, will build all firmware for all drivers 17enabled which ship its firmware inside the Linux kernel source tree. 18 19There are a few reasons why you might want to consider building your firmware 20into the kernel with CONFIG_EXTRA_FIRMWARE though: 21 22* Speed 23* Firmware is needed for accessing the boot device, and the user doesn't 24 want to stuff the firmware into the boot initramfs. 25 26Even if you have these needs there are a few reasons why you may not be 27able to make use of built-in firmware: 28 29* Legalese - firmware is non-GPL compatible 30* Some firmware may be optional 31* Firmware upgrades are possible, therefore a new firmware would implicate 32 a complete kernel rebuild. 33* Some firmware files may be really large in size. The remote-proc subsystem 34 is an example subsystem which deals with these sorts of firmware 35* The firmware may need to be scraped out from some device specific location 36 dynamically, an example is calibration data for for some WiFi chipsets. This 37 calibration data can be unique per sold device. 38 39