drm/i915: Pass timeout==0 on to i915_gem_object_wait_fence()

The i915_gem_object_wait_fence() uses an incoming timeout=0 to query
whether the current fence is busy or idle, without waiting. This can be
used by the wait-ioctl to implement a busy query.

Fixes: e95433c73a11 ("drm/i915: Rearrange i915_wait_request() accounting with callers")
Testcase: igt/gem_wait/basic-busy-write-all
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: <drm-intel-fixes@lists.freedesktop.org> # v4.10-rc1+
Cc: stable@vger.kernel.org
Link: http://patchwork.freedesktop.org/patch/msgid/20170212215344.16600-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -441,7 +441,7 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 			timeout = i915_gem_object_wait_fence(shared[i],
 							     flags, timeout,
 							     rps);
-			if (timeout <= 0)
+			if (timeout < 0)
 				break;
 
 			dma_fence_put(shared[i]);
@@ -454,7 +454,7 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 		excl = reservation_object_get_excl_rcu(resv);
 	}
 
-	if (excl && timeout > 0)
+	if (excl && timeout >= 0)
 		timeout = i915_gem_object_wait_fence(excl, flags, timeout, rps);
 
 	dma_fence_put(excl);