[Mesa-dev] Proposal to branch off old drivers

[Alex Deucher]

On Thu, May 25, 2017 at 8:45 PM, Timothy Arceri <tarceri at itsqueeze.com> wrote:
> Hi all,
>
> Following on from the discussion here:
>
> https://lists.freedesktop.org/archives/mesa-dev/2017-May/155971.html
>
> Back in 2011/12 despite various concerns old hardware would become useless,
> dropping support for DRI1 drivers Mesa proved distros were up to the
> challenge of packaging up the old driver branch, and since we maintain
> compatibility they continue to work without issue.
>
> I'm currently working on uniform packing for gallium drivers which means
> updates to struct gl_program_parameter_list and the assumption that
> everything is padded to 4 vectors. Rather than updating and testing i915 to
> work with this (or even hacking around it), I'd rather make the proposal to
> branch off some older drivers.
>
> Why branch them off?
>
> 1. IMO there is a bunch of clean-up this would enable such as:
>
> - enabling a bunch of extensions by default and removing on the runtime
> checks for these pasted all over the api.
> - dropping a bunch of non asm mesa ir code paths
> - dropping a bunch of driver function callbacks
> - the software tnl code??
> - Likely a bunch of other bits and pieces.
>
> 2. They are either not in development at all, or being updated extremely
> rarely. Testing is often just does this code compile. Having them in master
> just opens them to the possibility of breakage.
>
> 3. Death by a thousand cuts. While the clean-ups above may not be huge I
> would argue a more important outcome is the ability to preform re-factors,
> add features, etc without needlessly updating these drivers.
>
> As someone who re-factored the main gl_* structs last year in the lead up to
> shader cache support, I can say my job would have been much easier if I
> didn't have to needlessly update the old classic drivers.
> On the gallium side there is are things like adding caps to all the drivers
> etc, again not huge but another cut.
>
> 4. As the API expands it just adds more overhead for features these drivers
> will mostly never support. The drivers likely already run on systems with
> much slower cpus.
>
> My specific proposal is:
>
> - Rather than just pointing distros at the last Mesa release as we did for
> the DRI1 driver, we create a mesa-pre-dx9-1.0 branch (branched from 17.1).
> However unlikely this will at least give us the possibility to release
> updates as some dev's have shown interest in.
>
> - Remove the following drivers from master:
>    Classic:
>    --------
>    i915, nouveau, r200, radeon, swrast (classic)
>
>    Gallium:
>    --------
>    r300, i915g
>
> Opinions?

I think you are just creating work for yourself.  Realistically, who
is going to maintain this branch?  No one maintains these drivers in
master other then touching them when interfaces change.  We might as
well just drop them.  If anyone wants them, they can use an old
version of mesa.

Alex