1 =================== 2 Firmware Guidelines 3 =================== 4 5 Users switching to a newer kernel should *not* have to install newer 6 firmware files to keep their hardware working. At the same time updated 7 firmware files must not cause any regressions for users of older kernel 8 releases. 9 10 Drivers that use firmware from linux-firmware should follow the rules in 11 this guide. (Where there is limited control of the firmware, 12 i.e. company doesn't support Linux, firmwares sourced from misc places, 13 then of course these rules will not apply strictly.) 14 15 * Firmware files shall be designed in a way that it allows checking for 16 firmware ABI version changes. It is recommended that firmware files be 17 versioned with at least a major/minor version. It is suggested that 18 the firmware files in linux-firmware be named with some device 19 specific name, and just the major version. The firmware version should 20 be stored in the firmware header, or as an exception, as part of the 21 firmware file name, in order to let the driver detact any non-ABI 22 fixes/changes. The firmware files in linux-firmware should be 23 overwritten with the newest compatible major version. Newer major 24 version firmware shall remain compatible with all kernels that load 25 that major number. 26 27 * If the kernel support for the hardware is normally inactive, or the 28 hardware isn't available for public consumption, this can 29 be ignored, until the first kernel release that enables that hardware. 30 This means no major version bumps without the kernel retaining 31 backwards compatibility for the older major versions. Minor version 32 bumps should not introduce new features that newer kernels depend on 33 non-optionally. 34 35 * If a security fix needs lockstep firmware and kernel fixes in order to 36 be successful, then all supported major versions in the linux-firmware 37 repo that are required by currently supported stable/LTS kernels, 38 should be updated with the security fix. The kernel patches should 39 detect if the firmware is new enough to declare if the security issue 40 is fixed. All communications around security fixes should point at 41 both the firmware and kernel fixes. If a security fix requires 42 deprecating old major versions, then this should only be done as a 43 last option, and be stated clearly in all communications. 44
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.