Documentation/driver-api/firmware/built-in-fw.rst

File Facts

System

Linux kernel

Corpus path

Documentation/driver-api/firmware/built-in-fw.rst

Extension

.rst

Size

1312 bytes

Lines

34

Domain

Support Tooling And Documentation

Bucket

Documentation

Inferred role

Support Tooling And Documentation: documentation

Status

atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

• Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

• No C-style include directives detected by the generator.

Detected Declarations

• No top-level syscall, struct, function, initcall, or export declaration detected by the generator.

Annotated Snippet

=================
Built-in firmware
=================

Firmware can be built-in to the kernel, this means building the firmware
into vmlinux directly, to enable avoiding having to look for firmware from
the filesystem. Instead, firmware can be looked for inside the kernel
directly. You can enable built-in firmware using the kernel configuration
options:

  * CONFIG_EXTRA_FIRMWARE
  * CONFIG_EXTRA_FIRMWARE_DIR

There are a few reasons why you might want to consider building your firmware
into the kernel with CONFIG_EXTRA_FIRMWARE:

* Speed
* Firmware is needed for accessing the boot device, and the user doesn't
  want to stuff the firmware into the boot initramfs.

Even if you have these needs there are a few reasons why you may not be
able to make use of built-in firmware:

* Legalese - firmware is non-GPL compatible
* Some firmware may be optional
* Firmware upgrades are possible, therefore a new firmware would implicate
  a complete kernel rebuild.
* Some firmware files may be really large in size. The remote-proc subsystem
  is an example subsystem which deals with these sorts of firmware
* The firmware may need to be scraped out from some device specific location
  dynamically, an example is calibration data for some WiFi chipsets. This
  calibration data can be unique per sold device.

Annotation

• Atlas domain: Support Tooling And Documentation / Documentation.
• Implementation status: atlas-only.

Implementation Notes

• This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
• Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
• Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.