Radeon DRM GART mapping bogosity

[Benjamin Herrenschmidt]

On Tue, 2005-05-03 at 10:41 +0200, Jerome Glisse wrote:
> > Now, the setting above has to be done the most intelligently you can
> > based on 1) do you need 2 apertures with different swapper settings
> > (typical of BE machines) or not, 2) what is your CONFIG_APER_SIZE
> > strapping vs. how much VRAM you have ... You can see both kind of setups
> > on Mac cards.
> 
> Thx a lot for your explanation. A little question why 2 apertures are more
> typical on BE devices ? Having 2 apertures is the best way to handle
> dual head, isn't it (one for each head) ?

That allows you to have a different swapper setting for each aperture,
which is handy when your host is just directly accessing the frame
buffer. A BE host need a different setting most of the time for
different bit depths.

> If my memory isn't too corrupted you said that stupid pc card
> haven't CONFIG_APER_SIZE set to half of memory, does this
> really matter (I guess that this push you to map aperture to same
> area) ?

In fact, stupid Mac cards neither in some cases. If it is == to vram or
== to vram/2, it's fine. Anything else can be source of trouble. Though
in the case of little endian peecees, it may not be -that- bad.

Ben.