Re: [Linux-fbdev-devel] drm_fb_helper: Impossible to change video

["Michel Dänzer" <michel@daenzer.net>]

On Mon, 2010-03-15 at 18:38 +0000, James Simmons wrote: 
> > > The big issue we have with resizing the buffer is userspace mmaps of the fbdev
> > > device, and invalidation.
> > > Previous thread of unresolvedness is here.
> > > http://www.mail-archive.com/dri-devel@lists.sourceforge.net/msg41878.html
> > 
> > Actually AFAIR (and reading through it again seems to confirm this)
> > userspace mappings should be fully handled by the last patch series I
> > posted back then[0]. The problem was that the struct fb_ops hooks may be
> > called by the kernel from pretty much any context, and neither I nor
> > Thomas was sure how to handle the TTM locking given that. Maybe James
> > has ideas for this given his better familiarity with fbdev internals.
> 
> The fb_ops can only be called from fbcon or the fbdev userland interface. 
> The fbcon calls should only happen when the VC is in KD_TEXT mode. Now 
> with the DRM backend we have the advantage of creating a mapping seperate 
> from the console mapping. A fb_open/fb_close could be used to cleaning up 
> the userland mmap as well as handle the console pinning. We can supply 
> your own fb_mmap hook.

Again, the issue is not userspace but that fb_ops hooks can be called
from interrupt context etc.


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