[PATCH] drm: Initial KMS driver for AST (ASpeed Technologies) 2000 series

Michel Dänzer michel at daenzer.net
Tue Apr 24 07:28:30 PDT 2012

On Mon, 2012-04-23 at 14:30 +0100, Alan Cox wrote:
> > fbdev objects once exposed to userspace or to fbcon, thanks to some wonderful
> > API design way back, the mmaps on the fbdev device are direct to the VRAM
> > physical pages. Can't tear them down and move them into system RAM pages
> > at all easily.
> Thats not strictly true. They can move mapping if the locking is right
> and the helpers handle it because you can invalidate the pages in the
> userspace mappings and they will get faulted back with the new ones.

fbdev userspace mappings is the easy part, TTM has supported that for
years. The problem is fbcon, which can access the framebuffer from
basically any context for printk. 

> > Because I'm not 100% sure nothing will get written to it, and if
> Fair point.
> > something gets written
> > to it I'd rather not have to complicate the oops printing to have to
> > page in memory
> > from disk, when it might be the disk that caused the oops.
> If the box was horked that way then you are going to fail to migrate the
> graphical frame buffer out in order to go into text mode to print the
> oops. Probably safest any oops hits the current visible object ?

It's not always that simple either, e.g. this wouldn't work when
scanning out a tiled buffer on Radeon HDs.

Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer

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