DRI2 Protocol Spec Draft

[Michel Dänzer]

On Thu, 2008-09-11 at 11:59 -0400, Kristian Høgsberg wrote:
> 
> > On Wed, 2008-09-10 at 14:16 -0400, Kristian Høgsberg wrote:
> >> On Tue, Sep 9, 2008 at 1:34 PM, Michel Dänzer
> >> <michel at tungstengraphics.com> wrote:
> >> >
> >> > If the GLX implementation is to use DRI2CopyRegion for synchronization
> >> > purposes, then the interface of the latter needs to be at least as
> >> > expressive as the DRM synchronization interfaces currently used by the
> >> > former.
> >>
> >> Could you give a quick summary of what those are and where you think
> >> DRI2CopyRegion falls short?
> >
> > See e.g. intelScheduleSwap() in
> > mesa/src/mesa/drivers/dri/intel/intel_buffers.c:
> >
> >      * For the case of missing the target, chooses to accept tearing or
> >        execute the swap during the next vblank period (based on driconf
> >        vblank_mode).
> >      * Chooses the primary or secondary CRTC.
> >      * Needs the returned effective/expected sequence number to know if
> >        the target was hit or missed and to calculate the next target
> >        sequence number.
> >
> > The MSC related APIs as in mesa/src/mesa/drivers/dri/common/vblank.c
> > also need to be consistent with the DRI2CopyRegion sequence numbers. So
> > I think DRI2 would need to wrap the DRM_IOCTL_WAIT_VBLANK functionality
> > as well (or be DRM specific, which would be unfortunate - and could
> > still have issues like mapping the CRTC IDs between the DRM and DRI2
> > interfaces).
> 
> So we need to be able to specify whether to drop a frame or postpone
> it when we miss the target.  I'm not happy about having to return the
> effective swap sequence number... 

What is your concern?

> is there a way we can move the computation of the next target to the
> server?

Look at the GLX_OML_sync_control spec for example; if DRI2CopyRegion
doesn't provide feedback, wouldn't we have to move most if not all the
logic for this and similar extensions into the DRI2 server side?


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