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1===================2Firmware Guidelines3===================4 5Users switching to a newer kernel should *not* have to install newer6firmware files to keep their hardware working. At the same time updated7firmware files must not cause any regressions for users of older kernel8releases.9 10Drivers that use firmware from linux-firmware should follow the rules in11this guide. (Where there is limited control of the firmware,12i.e. company doesn't support Linux, firmwares sourced from misc places,13then of course these rules will not apply strictly.)14 15* Firmware files shall be designed in a way that it allows checking for16 firmware ABI version changes. It is recommended that firmware files be17 versioned with at least a major/minor version. It is suggested that18 the firmware files in linux-firmware be named with some device19 specific name, and just the major version. The firmware version should20 be stored in the firmware header, or as an exception, as part of the21 firmware file name, in order to let the driver detact any non-ABI22 fixes/changes. The firmware files in linux-firmware should be23 overwritten with the newest compatible major version. Newer major24 version firmware shall remain compatible with all kernels that load25 that major number.26 27* If the kernel support for the hardware is normally inactive, or the28 hardware isn't available for public consumption, this can29 be ignored, until the first kernel release that enables that hardware.30 This means no major version bumps without the kernel retaining31 backwards compatibility for the older major versions. Minor version32 bumps should not introduce new features that newer kernels depend on33 non-optionally.34 35* If a security fix needs lockstep firmware and kernel fixes in order to36 be successful, then all supported major versions in the linux-firmware37 repo that are required by currently supported stable/LTS kernels,38 should be updated with the security fix. The kernel patches should39 detect if the firmware is new enough to declare if the security issue40 is fixed. All communications around security fixes should point at41 both the firmware and kernel fixes. If a security fix requires42 deprecating old major versions, then this should only be done as a43 last option, and be stated clearly in all communications.44 45