Xserver driver merging pros & cons

[Dave Airlie]

On Thu, Sep 15, 2011 at 5:34 PM, Alex Deucher <alexdeucher at gmail.com> wrote:
> On Thu, Sep 15, 2011 at 11:45 AM, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
>> At XDC this week we discussed merging drivers back into the server
>> tree.  One thing I found frustrating about the discussion was that we
>> didn't have a whiteboard nor a list of the pros & cons of such a
>> change.  So I'd like to capture that here (from memory) to let us
>> continue the discussion about whether it's worth it or not.
>>
>> Luc, I think you're the most vocal opponent of this move, so I've cc'd
>> you so you can enumerate any issues I've forgotten.
>>
>> Anyway, as I recall, the issues are as follows:
>>
>> Pros:
>>  1) easier to propagate API changes across drivers (just like Linux)
>>     1a) thus easier to change ABI
>>  2) developers focused on driver development now have more incentive
>>     to make sure the server works well so regular releases can still
>>     happen (i.e. more people working on blockers whether driver or not
>>     as releases approach)
>>  3) allows removal of driver compat code for various server versions
>>     3a) thus removes combinations of driver+server that developers
>>         have to support & test
>>  4) increased test coverage for the server as users wanting current
>>     driver code will be building new servers too
>>
>> Cons:
>>  1) more work for distros to backport just driver changes to old
>>     servers (especially if people follow through on (3) above)
>>     1a) if backporting is harder, new hardware support will be more
>>         difficult to land in "enterprise" level distros
>>  2) harder for users to just upgrade drivers independently, now
>>     they'll have to build the whole server
>>     2a) thus less testing of current driver code from technical users
>>
>> I've already made my views pretty clear; I'd prefer merging the drivers
>> back in.  But I don't do as much work on the DIX or DDX as I used to,
>> and lots of others would be affected as well, so I'd like to hear what
>> people think.  Have I captured the pros & cons fully?  What to distro
>> maintainers think?  And driver developers, both input & output?
>
> For me personally, I don't seem much advantage in moving the drivers
> into the xserver.  The number of ABI breaks is minimal (usually 1 per
> xserver) and those can usually be fixed within a day or so of the
> breakage.  I don't rebuild the xserver nearly as often as I rebuild
> the ddx so it would mean more work to keep up with the xserver changes
> on a regular basis.  For unmaintained drivers, this might be an
> advantage, but at this point the unmaintained drivers are just about
> all for hardware >10 years old, so I'm not sure how important it is to
> continue to pretend we still support them.
>
> Additionally, as was shown in Jeremy's slides, the number of changes
> in the Xserver has been going down with each successive release.  It
> doesn't seem untenable to keep maintained external drivers in sync.
>

At the moment I have a large project in the works to redo the driver ABI,
its pretty much an impossible project no matter what happens, its a major
ABI change and will pretty much require major reworks off all the drivers.

Now I've no idea how to do this with the current model, even with the drivers
merged its going to be a real pain to land, thats if I ever even get
it to a useable
stage.

Dave.