drm/i915: Eliminate the trylock for awaiting an earlier request
We currently use an error-prone mutex_trylock to grab another timeline to find an earlier request along it. However, with a bit of a sleight-of-hand, we can reduce the mutex_trylock to a spin_lock on the immediate request and careful pointer chasing to acquire a reference on the previous request. Signed-off-by:Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by:
Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20191216165317.2742896-1-chris@chris-wilson.co.uk
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