[Mesa-dev] Proposal to branch off old drivers

[Marek Olšák]

On May 26, 2017 2:45 AM, "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


No matter how hard you are trying, there is no real benefit in removing any
Gallium drivers. Come on, is the PIPE_CAP thing your only argument? I can
add a new PIPE_CAP case to all gallium drivers in 15 seconds. If you can't
do that, you need a better editor.

The only reason for removing a Gallium driver would be if the driver was
broken or inferior in some way. That might be i915g, but even that is kinda
a shaky ground.

I thought you'd only ask about removing pre-i915 classic drivers (i.e.
keeping i915). That would have a higher chance of success.

Speaking of those, I think the deprecation branch could be 17.1 itself.

Marek


Opinions?
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