[PATCH 0/7] drm/vblank: timer: Fix timestamps and improve reliabilty

[Thomas Zimmermann <tzimmermann@suse.de>]

It appears that the DRM's vblank timers have always been somewhat buggy
in their timestamp calculations. Fix the generic implementation and
improve reliability.

Patch 1 returns success/failure to the caller, as expected by DRM.

Patch 2 fixes the timestamp calculation to return the time of the first
visible scanline in the current vblank phase.

Patch 3 switches the hrtimer to absolute values since boot, so that it's
easier to work with and we can predict future timestamps reliably.

Patches 4 and 5 allow for estimating timestamps even with the timer
being disabled.

Patches 6 and 7 improve the retrieval of the next vblank timeout's
timestamp.

Tested under heavy CPU-load on bochs and virtio. No ersors or warnings
showed up.

There have been reports about vblank timeouts being handled so late,
that they trigger DRM's internal error checks. Maybe these fixes and
adjustments can help to further avoid hick ups from delayed vblank
timers.

Thomas Zimmermann (7):
  drm/vblank: timer: Return success status from get_vblank_timeout
  drm/vblank: timer: Fix timestamp calculation
  drm/vblank: timer: Use absolute timer since boot
  drm/vblank: timer: Reorganize get_vblank_timeout
  drm/vblank: timer: Estimate vblank timeout if timer is disabled
  drm/vblank: timer: Verify that expiry time is in the future
  drm/vblank: timer: Avoid reading the vblank time unnecessarily

 drivers/gpu/drm/drm_vblank.c        | 105 ++++++++++++++++++++--------
 drivers/gpu/drm/drm_vblank_helper.c |   4 +-
 include/drm/drm_vblank.h            |   2 +-
 3 files changed, 79 insertions(+), 32 deletions(-)


base-commit: 4f554688dffcacf48630c14f9fb77a9f60394c1c
-- 
2.54.0