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Re: TiBook Dual Display

On Thu, 2001-10-18 at 09:46, Michael Schmitz wrote: 

> > > Lack of developer manpower (did you just volunteer to do it?). The
> > > technical specs are available to XFree members, the kernel infrastructure
> > > required to support mutiple framebuffers is in place for ages. Just make
> > > aty128fb register two separate framebuffers,
> > 
> > I question if it would be a good idea to do it on the framebuffer
> > device level at this time, because you'd have to either virtualize the
> > the accel engine or only be able to use acceleration on one head in X,
> > partition the video RAM statically between the heads, ...
> Sure, as a first approximation I'd perhaps recommend to go without
> acceleration anyway. I'm not sure how much more synchronization than plain
> 'wait until accel idle' would be required (which happens anyway IIRC). 

You don't necessarily have to wait for the engine to be idle. You do have to
realize the current context isn't the one of the head you want to do an
operation on. If you want to do that transparently inside the framebuffer
device, you have to map the MMIO area twice and fault on access to the
inactive one, saving and restoring registers which could make a difference,
potentially all of them. I doubt that would be very efficient.

The X server driver can do it much more efficiently, it only needs a
semaphore to detect when it has to reinitialize the context for a head, which
only involves setting the registers which are really needed.

> Static partitioning of vram is a given in that setup -

The X server could theoretically use the video RAM more efficiently
because it knows what it wants to do. In practice, I don't think the
infrastructure for this is in place yet, so I agree it's not important for

> I'd consider it a Big Problem as soon as XFree86 can switch color depth
> on the fly :-)

Expect that to happen sooner rather than later. I don't know if the Resize
and Rotate extension will be in 4.2.0 but it's certainly possible.

> > > X gurus please correct me if the current X release already supports
> > > Xinereama on rage128 out of the box

Actually, that's the wrong question BTW. Xinerama is a driver independent
extension. My answer is to a question along the lines of 'does the r128
driver support single-chip dualhead', which I'm sure you really meant to ask.

> > It doesn't, but Ani was working on it at one point. Don't know if he's
> > got anything working yet.
> We'll hear about that from him, I'm sure. 

He's not subscribed to this list though AFAIK.

Earthling Michel Dänzer (MrCooper)/ Debian GNU/Linux (powerpc) developer
XFree86 and DRI project member   /  CS student, Free Software enthusiast

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