[Intel-gfx] [RFC] GuC firmware versioning change

[Jeff McGee]

On Fri, Oct 12, 2018 at 01:51:46PM -0700, Rodrigo Vivi wrote:
> On Fri, Oct 12, 2018 at 01:24:30PM -0700, Jeff McGee wrote:
> > The GuC firmware team is proposing a change to the firmware versioning scheme.
> > The goal is to more accurately track the firmware interface to help users
> > manage dependencies on that interface. The proposed scheme is based on
> > semver.org with some additions to handle branching.
> > 
> > The proposed version number would have 4 fields: BASE.MAJOR.MINOR.PATCH.
> > Contrast this with the 2 fields in the current version number: MAJOR.MINOR.
> > Side note, the current firmware encodes a BRANCH and CLIENT number as well, but
> > they have not been needed by i915. So a firmware released with the proposed
> > scheme would be named <platform>_guc_ver<base>_<major>_<minor>_<patch>.bin
> > (ex: skl_guc_ver1_5_4_7.bin) instead of the current
> > <platform>_guc_ver<major>_<minor>.bin (ex: skl_guc_ver9_33.bin).
> > 
> > The BASE number is an ID that is used to identify a set of releases in which
> > the MAJOR.MINOR.PATCH semantics are consistent. In other words, two releases
> > from the same BASE can be compared via their MAJOR.MINOR.PATCH to infer their
> > relationship as described below. Two releases from a different BASE cannot be
> > reliably compared. The BASE number facilitates arbitrary branching which can
> > create duplicate and/or disconnected MAJOR.MINOR.PATCH versions. This type of
> > branching is expected to be rare, and so BASE will rarely change. When a new
> > BASE is created, the MAJOR.MINOR.PATCH reset to starting values.
> 
> Could you please clarify a bit what BASE means?
> What would be a different BASE?
> 

The BASE number supports general branching that would cause version number
conflicts. Branching for firmware releases is not desirable, but it is a
practical reality. Therefore the versioning scheme must accomodate it. Let's
say that a high-priority request is made to put specific updates on an old
release that said customer is locked on. Those updates could include any sort
of change including interface change. Then we have a sequence like below:

v1.1.0.0   v1.1.0.1   v1.1.0.2   v1.1.0.3   v1.1.1.0
----O----------O----------O----------O----------O
                           \
                            \
                             \
                              O----------O
                          v2.1.1.0   v2.1.1.1

You can see that if we don't have a BASE number that changes from 1 to 2, then
we end up with duplicated v1.1.0 along the different branches which are not the
same. As I wrote, this should be a very rare scenario, but it can happen. Maybe
upstream will always be supplied with releases from the "main" BASE, and you
can ignore this field, but it needs to be there for other firmware
distributions.
-Jeff

> > 
> > The MAJOR number conforms to the major in semver.org. It increments on a
> > backwards incompatible change of the interface. It resets to 1 on a change of
> > BASE. The MAJOR number basically works the same between the current and
> > proposed versioning schemes.
> > 
> > The MINOR number conforms to the minor in semver.org. It increments on a
> > backwards compatible change of the interface (new interfaces that are optional
> > to use). It will also increment on substantial new internal functionality that
> > doesn't affect the interface but should be called out to the user. It resets to
> > 0 on a change of MAJOR. The MINOR number in the current versioning scheme
> > increments on any backwards compatible change. The proposed versioning scheme
> > breaks this into the MINOR number just described and the PATCH number below.
> > 
> > The PATCH number conforms to the patch in semver.org. It increments on a
> > backwards compatible internal change, usually a bug fix. It resets to 0 on a
> > change of MINOR.
> 
> I like the idea of MAJOR.MINOR.PATCH following semver.org.
> 
> I think if we remove the BASE out of picture and just use semver clear,
> but maybe it is just because I didn't quite understand BASE.
> 
> > 
> > The MAJOR.MINOR collectively define the interface version. Because the MINOR
> > may also increment on a substantial internal change, it doesn't always mark an
> > interface change, e.g. 4.5 and 4.6 may have identical interfaces. But the
> > determination of interface compatibility is unchanged, e.g. 4.6 is always
> > backwards compatible with 4.5.
> > 
> > Each MAJOR.MINOR may continue to receive internal fixes along a branch even
> > after the main branch for that BASE has moved on to another MAJOR.MINOR.
> > Releases from these fix-only branches increment only the PATCH number on that
> > MAJOR.MINOR, and therefore remain semantically consistent with the main branch.
> > No change of BASE is therefore needed. Consider an example:
> > 
> > v1.1.0.0   v1.1.0.1   v1.1.0.2   v1.1.1.0   v1.1.1.1
> > ----O----------O----------O----------O----------O    <-- main adopts v1.1.1.x
> >                            \
> >                             \
> >                              \
> >                               O----------O     <-- fixes for interface v1.1.0.x
> >                           v1.1.0.3   v1.1.0.4
> 
> This approach is cool and more or less how Mesa handles their releases,
> except by the fact that their Major is the year and minor is the month.
> 
> However, on the firmware side I have a concern because we are so far trying
> to make sure that we have 1-1 relationship on kernel-firmware version.
> 
> But based on this view and what Anusha told me yesterday it seems
> that GuC is getting constant releases. With the constant patches we will
> soon explode linux-firmware.git repository size.
> 
> But this maybe is something to be solved on linux-firmware side and we make
> sure that we clean up and remove firmware that were never released in any
> official Linux kernel. Anusha or Antonio, thoughts?
> 
> Thanks,
> Rodrigo.
> 

I expect that i915 will still require a single version of firmware per platform
as it does today. This change should not impact that other than to require i915
to check 4 numbers instead of 2.

It is true that firmware releases are made *internally* (from the firmware
team to the operating system teams) at a frequent rate. It is up to each OS
team to decide their own cadence for integrating and distributing those
firmware based on their unique situation. So the Linux team may filter these
releases and update the upstream much less frequently.

> > 
> > There is no need to change the BASE because the branching happened from the
> > last fix (v1.1.0.2) on the main branch prior to the change of interface
> > (v1.1.1.0). As long as only fixes are applied to v1.1.0.x, there is no risk of
> > version number clash. All of these release versions remain semantically
> > connected with one small caveat. If this set of release versions came
> > sequentially along a single branch, one could infer that the exact fixes in
> > v1.1.0.4 were inherited by v1.1.1.0. With this "hidden" branching, this may
> > not be true as in this example. One would need to review the v1.1.1.0 release
> > notes to check.
> > 
> > Please provide any feedback on the proposed change.
> > 
> > Thanks,
> > Jeff