[PATCH] docs: driver-api: firmware: add driver firmware guidelines. (v2)

Dave Airlie
2022-07-19T06:54:36Z

From: Dave Airlie <airlied@redhat.com>

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.

Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
---
Documentation/driver-api/firmware/core.rst | 1 +
.../firmware/firmware-usage-guidelines.rst | 34 +++++++++++++++++++
2 files changed, 35 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..34d2412e78c6
--- /dev/null
+++ b/Documentation/driver-api/firmware/firmware-usage-guidelines.rst
@@ -0,0 +1,34 @@
+===================
+Firmware Guidelines
+===================
+
+Drivers that use firmware from linux-firmware should attempt to follow
+the rules in this guide.
+
+* Firmware should 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
+ major/minor/patch versions should be stored in a header in the
+ firmware file for the driver to detect any non-ABI fixes/issues. The
+ firmware files in linux-firmware should be overwritten with the newest
+ compatible major version. Newer major version firmware should remain
+ compatible with all kernels that load that major number.
+
+* Users should *not* have to install newer firmware to use existing
+ hardware when they install a newer kernel. If the hardware isn't
+ enabled by default or under development, 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 should be updated with the security fix, and 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