rjw | 1f88458 | 2022-01-06 17:20:42 +0800 | [diff] [blame^] | 1 | ================= |
| 2 | Built-in firmware |
| 3 | ================= |
| 4 | |
| 5 | Firmware can be built-in to the kernel, this means building the firmware |
| 6 | into vmlinux directly, to enable avoiding having to look for firmware from |
| 7 | the filesystem. Instead, firmware can be looked for inside the kernel |
| 8 | directly. You can enable built-in firmware using the kernel configuration |
| 9 | options: |
| 10 | |
| 11 | * CONFIG_EXTRA_FIRMWARE |
| 12 | * CONFIG_EXTRA_FIRMWARE_DIR |
| 13 | |
| 14 | This should not be confused with CONFIG_FIRMWARE_IN_KERNEL, this is for drivers |
| 15 | which enables firmware to be built as part of the kernel build process. This |
| 16 | option, CONFIG_FIRMWARE_IN_KERNEL, will build all firmware for all drivers |
| 17 | enabled which ship its firmware inside the Linux kernel source tree. |
| 18 | |
| 19 | There are a few reasons why you might want to consider building your firmware |
| 20 | into 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 | |
| 26 | Even if you have these needs there are a few reasons why you may not be |
| 27 | able 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 | |