On Wednesday, February 13, 2008 2:22 pm Stephane Marchesin wrote:
> On 2/13/08, Dave Airlie <[EMAIL PROTECTED]> wrote:
> > So I've been thinking about this stuff a lot lately wrt to getting the
> > DRM into a state that enables fast-user-switching, GPGPU apps,
> > different users on a per head one a single card..
> >
> > http://dri.freedesktop.org/wiki/DRMRedesign
> >
> > has a nice picture and some notes.. either comment direct on the webpage,
> > or reply here..
> >
> > A lot of the code heading in this direction just got merged into
> > modesetting-101, it should in theory all be backwards compat in the
> > single render/master case...
>
> Hi,
>
> So basically, you'd expose multiple /dev entries for a single piece of
> hardware. As I said on irc, this would be like exposing /dev/sda1_ext2
> and /dev/sda1_xfs and ... which obviously doesn't scale long-term.
>
> Lets forget about the concept of "master" for a moment. In a case
> where the concept of "master" does not exist, an application that can
> draw to screen (formerly "master") would simply be one that has a
> scanout BO and is using it.
>
> So here is the point: with the current work on enforcing proper
> permissions on BOs (including scanout BOs), is a separate device
> really needed ? The reason for doing this device separation in the
> first place basically comes down to enforcing those permissions
> properly in a per-app fashion. The same effect could be achieved by
> enforcing the policy on BO creation instead of device opening.

IIRC, the reason we came up with this was to deal with CRTC<->output mapping, 
not for BO permissions so much (doing proper perms there still requires a lot 
of work).

You don't want any application to be able to change CRTC<->output mappings, or 
bind BOs to CRTCs.  Ideally you'd just have one app that could do that on a 
given system, and it would contain the distribution's policy regarding output 
cloning, hotplug actions, etc.

So the master/slave concept is really more analogous to pty master & slave 
nodes than it is to your /dev/sda_ext3 example.  You open the master node, 
ask for a specific mapping, and if you have permission, a slave node will be 
created that you can do what you like with...

Jesse

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