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

[Dave Airlie <airlied@gmail.com>]

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.

I'm cc'ing this quite widely to reach subsystems which use fw a lot.

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