[Xorg] Getting GATOS branch created on Xorg

Jon Smirl jonsmirl at yahoo.com
Fri Aug 20 11:16:25 PDT 2004

--- Vladimir Dergachev <volodya at mindspring.com> wrote:
> On Fri, 20 Aug 2004, Jon Smirl wrote:
> > There is already code in X for coordinating video memory usage with
> > DRM. The DRM memory manager keeps 2D X from stomping on 3D buffers.
> > Same mechansim can be used to protect the video streaming memory.
> Last time I checked this was not straightforward. Furthermore, aren't
> 3d buffers fixed in size after Xserver startup ?

There is a DRM API for allocating VRAM memory from the pool assigned to
3D use. Just allocate yourself a chunk and don't start any 3D
operations on it. You get a pointer to it so you can do anything you
want with it.

> > Several other cards use kernel based v4l drivers, why is the radeon
> > special?
> I am only aware of bt848 cards - these are standalone video capture
> device and do not have to share anything.

Check out the Matrox implementation.

> Also, AIW cards do have a v4l interface - however it is an auxiliary 
> driver only, it needs Xv program to setup the video stream for any
> data to be available (this way it can use video memory already
> allocated by Xserver for video stream)

I always thought the best solution would be combining the radeon V4L
device driver into the radeon DRM driver. That way we only have a
single device driver trying to attach to the hardware. The combined
driver would expose two interfaces, DRM and V4L. Since the drivers are
combined you can easily sort out the memory allocation.

Have you tried doing the experiment of combining the radeon DRM and V4L
device drivers? I would start out by just mixing up all of the code.
But the final version should make the V4L support an add-on module to
the DRM one.

Jon Smirl
jonsmirl at yahoo.com

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