[Intel-gfx] [PATCH 5/5] drm/i915: Allow vblank interrupts during modeset and eliminate some vblank races

[Michel Dänzer]

On Mon, 2014-02-24 at 14:11 +0200, Ville Syrjälä wrote:
> On Mon, Feb 24, 2014 at 12:48:55PM +0900, Michel Dänzer wrote:
> > On Fre, 2014-02-21 at 21:03 +0200, ville.syrjala at linux.intel.com wrote:
> > > 
> > > We can kill of the drm_vblank_{pre,post}_modeset() calls since those are
> > > there simply to make drm_vblank_get() fail during a modeset.
> > 
> > Actually, their original purpose was to keep the DRM vblank counter
> > consistent across modesets, assuming the modeset resets the hardware
> > vblank counter.
> 
> I see. Well, actually I really don't. The code is too funky for me to
> tell what it actually ends up doing. The obvious way would be to
> resample the hardware counter at drm_vblank_post_modeset(), which the
> code certainly doesn't do. But maybe it did something sensible in the
> past.

When the pre/post-modeset hooks were originally added, it worked like
this: the pre-modeset hook enabled the vblank interrupt, which updated
the DRM vblank counter from the driver/HW counter. The post-modeset hook
disabled the vblank interrupt again, which recorded the post-modeset
driver/HW counter value.

But the vblank code has changed a lot since then, not sure it still
works like that.


-- 
Earthling Michel Dänzer            |                  http://www.amd.com
Libre software enthusiast          |                Mesa and X developer