| xj | b04a402 | 2021-11-25 15:01:52 +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 | There are a few reasons why you might want to consider building your firmware |
| 15 | into the kernel with CONFIG_EXTRA_FIRMWARE: |
| 16 | |
| 17 | * Speed |
| 18 | * Firmware is needed for accessing the boot device, and the user doesn't |
| 19 | want to stuff the firmware into the boot initramfs. |
| 20 | |
| 21 | Even if you have these needs there are a few reasons why you may not be |
| 22 | able to make use of built-in firmware: |
| 23 | |
| 24 | * Legalese - firmware is non-GPL compatible |
| 25 | * Some firmware may be optional |
| 26 | * Firmware upgrades are possible, therefore a new firmware would implicate |
| 27 | a complete kernel rebuild. |
| 28 | * Some firmware files may be really large in size. The remote-proc subsystem |
| 29 | is an example subsystem which deals with these sorts of firmware |
| 30 | * The firmware may need to be scraped out from some device specific location |
| 31 | dynamically, an example is calibration data for for some WiFi chipsets. This |
| 32 | calibration data can be unique per sold device. |
| 33 | |