| =================== |
| Firmware Guidelines |
| =================== |
| |
| Users switching to a newer kernel should *not* have to install newer |
| firmware files to keep their hardware working. At the same time updated |
| firmware files must not cause any regressions for users of older kernel |
| releases. |
| |
| Drivers that use firmware from linux-firmware should follow the rules in |
| this guide. (Where there is limited control of the firmware, |
| i.e. company doesn't support Linux, firmwares sourced from misc places, |
| then of course these rules will not apply strictly.) |
| |
| * Firmware files shall be designed in a way that it allows checking for |
| firmware ABI version changes. It is recommended that firmware files be |
| versioned with at least a major/minor version. It is suggested that |
| the firmware files in linux-firmware be named with some device |
| specific name, and just the major version. The firmware version should |
| be stored in the firmware header, or as an exception, as part of the |
| firmware file name, in order to let the driver detact any non-ABI |
| fixes/changes. The firmware files in linux-firmware should be |
| overwritten with the newest compatible major version. Newer major |
| version firmware shall remain compatible with all kernels that load |
| that major number. |
| |
| * If the kernel support for the hardware is normally inactive, or the |
| hardware isn't available for public consumption, this can |
| be ignored, until the first kernel release that enables that hardware. |
| This means no major version bumps without the kernel retaining |
| backwards compatibility for the older major versions. Minor version |
| bumps should not introduce new features that newer kernels depend on |
| non-optionally. |
| |
| * If a security fix needs lockstep firmware and kernel fixes in order to |
| be successful, then all supported major versions in the linux-firmware |
| repo that are required by currently supported stable/LTS kernels, |
| should be updated with the security fix. The kernel patches should |
| detect if the firmware is new enough to declare if the security issue |
| is fixed. All communications around security fixes should point at |
| both the firmware and kernel fixes. If a security fix requires |
| deprecating old major versions, then this should only be done as a |
| last option, and be stated clearly in all communications. |
| |
