Re: [linux-fbdev] New api again

[James S. <jsi...@su...>]

> what if i wanted to write a fbdev for, for example, the 3Dlabs Oxygen GVX420
> board ? 
> 
> For you information this board contains 3 different chip, A gamma 2 chip,
> acting as agp bridge and T&L engine, and 2 Permedia4 chips, doing 3D setup and
> rasterization. They can be configuredto be shared for rasterizing the same
> framebuffer, splitting the scanline between them, or to support dual head.

I assume T&L is texture and lighting engine. 

> Each Pm4 has one pipeline, i think.

First a pipeline is a collect of pipes. Each pipe takes data and changes
it a certain way. This occurs until we reach the end of the pipeline when
we get the final desired rastered image.

Well that depends. Can data be processed by one Pm4 chip and then passed
to the second Pm4 chip to be processed by another stage? A good example
would be say a triangle strip was passed to the the first chip to say be
rotated. Then that data is passed onto the second chip to be tranformed to
give the appearance of a prespective view. In this case their is one
pipeline with 2 pipes. Now if this doesn't occur and each chip processes
data independent of each other then their is two pipelines with one pipe
each. This is of course assuming each GPU, the Pm4's, can't handle more
than one graphics command at a time. Is the T&L shared between both
GPU's. I really have to look at the hardware specs to say exactly. As you
can see for a mor advance card like the Oxygen things get more a bit more
complex. 

> The additional problem, is that you can address the rasterizer chip either
> directly (they have FB and Command register pci aperture, and a separate pci
> id) or trough the Gamma chip, for example, for when doing 3D, you send command
> to the gamma, which process them (T&L) and then forward the low level commands
> to one or both Permedia4 chip. If you want ot use one or both accesses, you
> would need to synchronize correctly between them.

Okay I'm taking a shot in the dark since I don't have the specs but I'm 
assuming the Gamma chip is for DMA, especially since you mentioned that 
it manages the agp port, and the Command register space is for MMIO
programming. Yes you do you have to manage access to both of them. 
Internal to the fbdev driver this is pretty simple. When userland wants to
play around with this stuff then you need a RRM (rendering resource
manager) to balance access. As 2.4.X stands right now you can't use the 
DMA with fbcon but I will be working on this problem right now.