drm/i915/gt: Clear the execlists timers upon reset

Across a reset, we stop the engine but not the timers. This leaves a
window where the timers have inconsistent state with the engine, but
should only result in a spurious timeout. As we cancel the outstanding
events, also cancel their timers.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201204151234.19729-4-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -2450,6 +2450,11 @@ cancel_port_requests(struct intel_engine_execlists * const execlists)
 
 	smp_wmb(); /* complete the seqlock for execlists_active() */
 	WRITE_ONCE(execlists->active, execlists->inflight);
+
+	/* Having cancelled all outstanding process_csb(), stop their timers */
+	GEM_BUG_ON(execlists->pending[0]);
+	cancel_timer(&execlists->timer);
+	cancel_timer(&execlists->preempt);
 }
 
 static inline void