[Mesa-dev] [RFC] Concrete proposal to split classic

[Timothy Arceri]

On 3/23/21 7:26 PM, Ian Romanick wrote:

> I would like to wait a couple more releases to do this.  I have a couple
> things that I've been gradually working on for some of the non-i965
> classic drivers that I'd like to land before they're put out to pasture.
>   I talked to ajax about this a few weeks ago, and he was amenable at the
> time.

Is there any reason these could not just land in the forked classic 
branch? The consensus seems to be we would still be making the odd 
release of these forked drivers, unlike how the DRI1 drivers were put 
out to pasture. Ken already outlined a desire to still be able to add 
occasional features to i965.

There is real momentum around cleaning up and optimising core Mesa at 
the moment, I'd really hate to see that slow down just because of a self 
imposed rule on what changes can land in a forked classic branch. I 
can't see there being to many MRs and releases required whether we 
applied a strict "build and critical bug fixes only" policy or just let 
any reasonable MR be accepted. I mean its not like there are MR flowing 
in for classic drivers now.

Just to be clear I'm +1 for forking 21.1.

> On 3/22/21 3:15 PM, Dylan Baker wrote:
>> Hi list,
>>
>> We've talked about it a number of times, but I think it's time time to
>> discuss splitting the classic drivers off of the main development branch
>> again, although this time I have a concrete plan for how this would
>> work.
>>
>> First, why? Basically, all of the classic drivers are in maintanence
>> mode (even i965). Second, many of them rely on code that no one works
>> on, and very few people still understand. There is no CI for most of
>> them, and the Intel CI is not integrated with gitlab, so it's easy to
>> unintentionally break them, and this breakage usually isn't noticed
>> until just before or just after a release. 21.0 was held up (in small
>> part, also me just getting behind) because of such breakages.
>>
>> I konw there is some interest in getting i915g in good enough shape that
>> it could replace i915c, at least for the common case. I also am aware
>> that Dave, Ilia, and Eric (with some pointers from Ken) have been
>> working on a gallium driver to replace i965. Neither of those things are
>> ready yet, but I've taken them into account.
>>
>> Here's the plan:
>>
>> 1) 21.1 release happens
>> 2) we remove classic from master
>> 3) 21.1 reaches EOL because of 21.2
>> 4) we fork the 21.1 branch into a "classic-lts"¹ branch
>> 5) we disable all vulkan and gallium drivers in said branch, at least at
>>     the Meson level
>> 6) We change the name and precidence of the glvnd loader file
>> 7) apply any build fixups (turn of intel generators for versions >= 7.5,
>>     for example
>> 8) maintain that branch with build and critical bug fixes only
>>
>> This gives ditros and end users two options.
>> 1) then can build *only* the legacy branch in the a normal Mesa provides
>>     libGL interfaces fashion
>> 2) They can use glvnd and install current mesa and the legacy branch in
>>     parallel
>>
>> Because of glvnd, we can control which driver will get loaded first, and
>> thus if we decide i915g or the i965 replacement is ready and turn it on
>> by default it will be loaded by default. An end user who doesn't like
>> this can add a new glvnd loader file that makes the classic drivers
>> higher precident and continue to use them.
>>
>> Why fork from 21.1 instead of master?
>>
>> First, it allows us to delete classic immediately, which will allow
>> refactoring to happen earlier in the cycle, and for any fallout to be
>> caught and hopefully fixed before the release. Second, it means that
>> when a user is switched from 21.1 to the new classic-lts branch, there
>> will be no regressions, and no one has to spend time figuring out what
>> broke and fixing the lts branch.
>>
>> When you say "build and critical bug fixes", what do you mean?
>>
>> I mean update Meson if we rely on something that in the future is
>> deprecated and removed, and would prevent building the branch or an
>> relying on some compiler behavior that changes, gaping exploitable
>> security holes, that kind of thing.
>>
>> footnotes
>> ¹Or whatever color you like your bikeshed
>>
>>
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