From: Dave Airlie Date: Thu, 21 Jul 2022 04:43:52 +0000 (+1000) Subject: docs: driver-api: firmware: add driver firmware guidelines. (v3) X-Git-Tag: v6.1-rc5~725^2~5 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=321eaf317dec3710e7a4ad3b3c363d9314c15195;p=platform%2Fkernel%2Flinux-starfive.git docs: driver-api: firmware: add driver firmware guidelines. (v3) A recent snafu where Intel ignored upstream feedback on a firmware change, led to a late rc6 fix being required. In order to avoid this in the future we should document some expectations around linux-firmware. I was originally going to write this for drm, but it seems quite generic advice. v2: rewritten with suggestions from Thorsten Leemhuis v3: rewritten with suggestions from Mauro Acked-by: Luis Chamberlain Acked-by: Rodrigo Vivi Acked-by: Daniel Vetter Acked-by: Harry Wentland Signed-off-by: Dave Airlie Link: https://lore.kernel.org/r/20220721044352.3110507-1-airlied@gmail.com Signed-off-by: Greg Kroah-Hartman --- diff --git a/Documentation/driver-api/firmware/core.rst b/Documentation/driver-api/firmware/core.rst index 1d1688c..803cd57 100644 --- a/Documentation/driver-api/firmware/core.rst +++ b/Documentation/driver-api/firmware/core.rst @@ -13,4 +13,5 @@ documents these features. direct-fs-lookup fallback-mechanisms lookup-order + firmware-usage-guidelines diff --git a/Documentation/driver-api/firmware/firmware-usage-guidelines.rst b/Documentation/driver-api/firmware/firmware-usage-guidelines.rst new file mode 100644 index 0000000..fdcfce4 --- /dev/null +++ b/Documentation/driver-api/firmware/firmware-usage-guidelines.rst @@ -0,0 +1,44 @@ +=================== +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. +