Re: radeon-pre-2

[Vladimir Dergachev]

Alan,
  I would like to disagree with you.

On Fri, 10 Sep 2004, Alan Cox wrote:

> On Gwe, 2004-09-10 at 23:19, Dave Airlie wrote:
> > If the kernel developers can address this point I would be most
> > interested, in fact I don't want to hear any more about sharing lowlevel
> > VGA device drivers until someone addresses why it is acceptable to have
> > two separate driver driving the same hardware for video and not for
> > anything else.. (remembering graphics cards are not-multifunction cards -
> > like Christoph used as an example before - 2d/3d are not separate
> > functions...)...
>
> We've addressed this before. Zillions of drivers provide multiple
> functions to multiple higher level subsystems. They don't all have to
> be compiled together to make it work.
>
> 2D and 3D _are_ to most intents and purposes different functions. They
> are as different as IDE CD and IDE disk if not more so.

Functions - yes, but they become such only at a higher level. 3d for 
example does not really exist in kernel in any form.

I would like to see unified fb (or the hardware-specific part of fb) and 
drm for one simple reason that I think you mentioned:

    One driver per device. I.e. one driver per *physical* device.

Lastly, one point that you appear to have missed: DRM does DMA transfers
(among everything else). FB sets video modes - i.e. messes with PLL.
The problem is that there are configurations where messing with PLL while 
a DMA trasfer is active will lock up PCI (or AGP) bus hard.

For example, a video decoder can be clocked off pixel clock for video pass 
through mode. If we trasfer video data to main RAM at the same time and
FB gets a command instructing it to change resolution there would be a 
hard lockup.

                          best

                            Vladimir Dergachev
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