[Mesa-dev] Proposal to branch off old drivers

[Timothy Arceri]

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?