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

[Rodrigo Vivi]

On Mon, Jul 18, 2022 at 05:21:44PM +1000, Dave Airlie wrote:
> From: Dave Airlie <airlied at 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 at 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.

would symbolic links be acceptable in the linux-firmware.git where
the <fmw>_<major>.bin is a sym link to <fwm>_<major>.<minor>.bin

or having the <fwm>_<major>.bin really to be the overwritten every minor
update?

> +
> +* 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.

Everything makes sense to me. Thanks for writing this down.

Acked-by: Rodrigo Vivi <rodrigo.vivi at intel.com>

> +
> -- 
> 2.36.1
> 
> 
> 
> --
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