Re: xf86-video-tegra or xf86-video-modesetting?

[Thierry Reding <thierry.reding-RM9K5IK7kjKj5M59NBduVrNAH6kLmebB@public.gmane.org>]

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On Sun, Nov 25, 2012 at 09:51:46PM -0500, Alex Deucher wrote:
> On Sat, Nov 24, 2012 at 4:09 PM, Thierry Reding
> <thierry.reding-RM9K5IK7kjKj5M59NBduVrNAH6kLmebB@public.gmane.org> wrote:
> > going into Linux 3.8 and NVIDIA posting initial patches
> > for 2D acceleration on top of it, I've been looking at the various ways
> > how this can best be leveraged.
> >
> > The most obvious choice would be to start work on an xf86-video-tegra
> > driver that uses the code currently in the works to implement the EXA
> > callbacks that allow some of the rendering to be offloaded to the GPU.
> > The way I would go about this is to fork xf86-video-modesetting, do some
> > rebranding and add the various bits required to offload rendering.
> >
> > However, that has all the usual drawbacks of a fork so I thought maybe
> > it would be better to write some code to xf86-video-modesetting to add
> > GPU-specific acceleration on top. Such code could be leveraged by other
> > drivers as well and all of them could share a common base for the
> > functionality provided through the standard DRM IOCTLs.
> >
> > That approach has some disadvantages of its own, like the potential
> > bloat if many GPUs do the same. It would also be a bit of a step back
> > to the old monolithic days of X.
> 
> Just fork and fill in your own GPU specific bits.  Most accel stuff
> ends up being very GPU specific.

That doesn't exclude the alternative that I described. Maybe I didn't
express what I had in mind very clearly. What I propose is to add some
code to the modesetting driver that would allow GPU-specific code to be
called if matching hardware is detected (perhaps as stupidly as looking
at the DRM driver name/version). Such code could perhaps be called from
the DDX' .ScreenInit and call the GPU-specific function to register an
EXA driver.

That would allow a large body of code (modesetting, VT switching, ...)
to be shared among a number of drivers instead of duplicating the code
for each one and having to keep merging updates from the modesetting
driver as it evolves. So the GPU-specific acceleration would just sit on
top of the existing code and only be activated on specific hardware.
What I'm *not* proposing is to create an abstraction layer for
acceleration.

Thierry

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