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Commit fdb68e09bbb1c981f24608d7022c7d93cc47b326

Authored by Mario Kleiner
Committed by Dave Airlie
1 parent 3790e395b8

drm: Zero out invalid vblank timestamp in drm_update_vblank_count. 

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 3.17, 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.

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: <stable@vger.kernel.org> #v3.17+

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

Showing 1 changed file with 4 additions and 5 deletions Side-by-side Diff

drivers/gpu/drm/drm_irq.c
Diff comments   View file @ fdb68e0
... ... @@ -131,12 +131,11 @@
131 131  
132 132 /* Reinitialize corresponding vblank timestamp if high-precision query
133 133 * available. Skip this step if query unsupported or failed. Will
134   - * reinitialize delayed at next vblank interrupt in that case.
  134 + * reinitialize delayed at next vblank interrupt in that case and
  135 + * assign 0 for now, to mark the vblanktimestamp as invalid.
135 136 */
136   - if (rc) {
137   - tslot = atomic_read(&vblank->count) + diff;
138   - vblanktimestamp(dev, crtc, tslot) = t_vblank;
139   - }
  137 + tslot = atomic_read(&vblank->count) + diff;
  138 + vblanktimestamp(dev, crtc, tslot) = rc ? t_vblank : (struct timeval) {0, 0};
140 139  
141 140 smp_mb__before_atomic();
142 141 atomic_add(diff, &vblank->count);