From: Dave Airlie <airlied@xxxxxxxxxx>
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 <mcgrof@xxxxxxxxxx>
Acked-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Acked-by: Daniel Vetter <daniel@xxxxxxxx>
Acked-by: Harry Wentland <harry.wentland@xxxxxxx>
Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
---
Documentation/driver-api/firmware/core.rst | 1 +
.../firmware/firmware-usage-guidelines.rst | 44 +++++++++++++++++++
2 files changed, 45 insertions(+)
create mode 100644 Documentation/driver-api/firmware/firmware-usage-guidelines.rst
diff --git a/Documentation/driver-api/firmware/core.rst b/Documentation/driver-api/firmware/core.rst
index 1d1688cbc078..803cd574bbd7 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 000000000000..fdcfce42c6d2
--- /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.
+
--
2.36.1
