Since commit 844b03f27739135fe1fed2fef06da0ffc4c7a081 we make sure that after vblank irq off, we return the last valid (vblank count, vblank timestamp) pair to clients, e.g., during modesets, which is good.
An overlooked side effect of that commit for kms drivers without support for precise vblank timestamping is that at vblank irq enable, when we update the vblank counter from the hw counter, we can't update the corresponding vblank timestamp, so now we have a totally mismatched timestamp for the new count to confuse clients.
Restore old client visible behaviour from before Linux 3.18, but zero out the timestamp at vblank counter update (instead of disable as in original implementation) if we can't generate a meaningful timestamp immediately for the new vblank counter. This will fix this regression, so callers know they need to retry again later if they need a valid timestamp, but at the same time preserves the improvements made in the commit mentioned above.
v2: Rebased on top of Daniel Vetter's fixup and documentation patch for timestamp updates. Drop request for stable kernel backport as this would be more difficult, unless the original patch would get applied to stable kernels.
Signed-off-by: Mario Kleiner mario.kleiner.de@gmail.com
Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: Daniel Vetter daniel@ffwll.ch Cc: Dave Airlie airlied@redhat.com --- drivers/gpu/drm/drm_irq.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index 152d1de..44e6a20b 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -161,10 +161,13 @@ static void drm_update_vblank_count(struct drm_device *dev, int crtc)
/* * Only reinitialize corresponding vblank timestamp if high-precision query - * available and didn't fail. Will reinitialize delayed at next vblank - * interrupt in that case. + * available and didn't fail. Otherwise reinitialize delayed at next vblank + * interrupt and assign 0 for now, to mark the vblanktimestamp as invalid. */ - store_vblank(dev, crtc, diff, rc ? &t_vblank : NULL); + if (!rc) + t_vblank = (struct timeval) {0, 0}; + + store_vblank(dev, crtc, diff, &t_vblank); }
/*