Xserver driver merging pros & cons
Peter Hutterer
peter.hutterer at who-t.net
Thu Sep 15 14:13:28 PDT 2011
On Thu, Sep 15, 2011 at 06:05:46PM +0100, Dave Airlie wrote:
> 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.
That should be the subject of a separate discussion then, to avoid the
conflation of the two issues.
Cheers,
Peter
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