[Linux-fbdev-devel] Re: FB model basic issues (WAS: radeon, apertures & memory mapping)

[Benjamin Herrenschmidt]

On Wed, 2005-03-16 at 21:51 +0200, Ville Syrjälä wrote:

> This was about the DirectFB drivers.
> 
> One thing just popped to my head though. If in the future we are going to 
> allow graphics cards to render to system memory, using the swapper will no 
> longer work. I don't see any other solution that having the CPU perform 
> the byte swapping.

There is a _lot_ of existing code that will stop working, MOL is an
example, it requires proper "native" format for the framebuffer. X too
in it's current incarnation (fb format is defined at compile time I
think).

So the swapper is _needed_ for framebuffer access.

The best we can do is save/change/restore it around accesses like we do
already when copying YUV frames to video memory.

Now regarding the setup of the apertures, I suppose that I'll do
something complicated that nobody will use right, that is use 2 separate
apertures contiguous with each framebuffer at the beginning of each
aperture when CONFIG_APER_SIZE is 1/2 of vram size, and 2 separate
apertures contiguous with each framebuffer together in the first one in
the other cases. Only difference: first case will allow macs to have
separate swappers for each aperture. All other cases will have both
swappers set the same way. Hopefully, all "Mac" cards have
CONFIG_APER_SIZE set to half the vram.

Ben.