Re: [RFC] enhancing the kernel's graphics subsystem

[Helge Hafting]

Dave Airlie wrote:
> On 5/21/07, Jon Smirl <jonsmirl@xxxxxxxxxxx> wrote:
> > On Thu, 17 May 2007 14:23:45 -0700, Jesse Barnes wrote:
> >
> > > In collaboration with the FB guys, we've been working on enhancing the
> > > kernel's graphics subsystem in an attempt to bring some sanity to the
> > > Linux graphics world and avoid the situation we have now where several
> > > kernel and userspace drivers compete for control of graphics devices.
> >
> > How is supporting different users logged into each head going to work?
> > The original model for this was to give each head its own fbdev device.
> > It is important that each user be able to set their own mode without 
> > being
> > root.
>
> TThe problem with that is the concept of heads is flawed... there is
> in reality no such
> thing, you have crtcs and outputs, no heads. So any attempt to enforce
> the head concept involves putting policy into the kernel, as if I have
> 3 outputs but 2 crtcs how do I decide the mappings without the admin
> telling the kernel,
Solution:
One device per crtc. You can then have two users, running consoles
or xservers on their crtcs, without having to involve root.

The crtc->output mapping must still be done by root of course.

This solution allow the useful case where the computer boots, the boot 
scripts
set up a crtc->output mapping. Then users log in through the
various consoles (using getty or xdm or similiar) using their grahphical
devices in whatever way they want.  A true multiseat setup.


And if one user needs to use all the screens for multi-display work?
Let root change the mappings, possibly through some sudo setup.

Helge Hafting
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