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

["Ville Syrjälä" <syrjala@sci.fi>]

On Thu, Mar 11, 2010 at 02:22:14AM +0000, James Simmons wrote:
> 
> > > > There are other drivers that support multihead already (matroxfb, any
> > > > other?) and have their own driver-specific inteface.
> > > 
> > > Each crtc is treated as a seperate fbdev device. I don't recall any 
> > > special ioctls. Maybe for mirroring which was never standardized.
> > 
> > matroxfb does have a bunch of custom ioctls to change the crtc<->output
> > mapping. 
> 
> Yes the mapping issue were never address.
> 
> > I don't think the CRTCû_info makes much sense if the main use
> > case is fbcon.
> 
> Actually that is what I had in mind when I reworked the fbdev api. Plus 
> with the linux console project I got multiple VTs working at the same 
> time.
> 
> > fbcon will use a single fb device and so you can't see
> > the console on multiple heads anyway which makes the whole thing
> > somewhat pointless. And if you're trying to do something more complex
> > you will be a lot better off bypassing fbdev altogether.
> 
> Not true. You can map different displays to different vcs. Give con2fb a 
> try some time :-)

I know about it but only one VT can be active at any given time.

> Now there is the issue of more than one keyboard being 
> mapped at a time. BTW I did getting multipe VT working at the same 
> time working in the past. It requires some cleanup on the console layer.

Well if you think that cleanup is possible and worth the effort then it
might make sense. The crtc<->output mapping is still unresolved though
and it depends on hardware which combinations are supported. If for
example the hardware can't drive multiple outputs with the same CRTC
or if the outputs require totally different timings then you can't
clone the same VT to multiple outputs.

-- 
Ville Syrjälä
syrjala@sci.fi
http://www.sci.fi/~syrjala/