drm/i915: fix up _wait_for macro
As Thomas Gleixner spotted, it's rather horrible racy: - We can miss almost a full tick, so need to compensate by 1 jiffy. - We need to re-check the condition when having timed-out, since a the last check could have been before the timeout expired. E.g. when we've been preempted or a long irq happened. Cc: Thomas Gleixner <tglx@linutronix.de> Reported-by: Jack Winter <jbh@alchemy.lu> Cc: Jack Winter <jbh@alchemy.lu> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
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