FB model basic issues (WAS: radeon, apertures & memory mapping)

[Benjamin Herrenschmidt]

> DirectFB assumes all memory outside var.yres_virtual * fix.line_length is 
> preserved. A totally valid assumption in my opinion. 

Except that you can't know in advance how much fix.line_length will be.
The "fix" isn't really "fixed". Different cards will have different
requirements depending on the bit depth for example. On radeonfb, the
line_length will vary due to alignment constraints related to the
engine, or due to tiling, etc.... etc...

So you basically don't know in advance what will be preserved... (And
you can't, unless you start having all sort of card specific knowledge).

 
Ben.