drm/i915: Enable i915_gem_wait_for_idle() without holding struct_mutex

The principal motivation for this was to try and eliminate the
struct_mutex from i915_gem_suspend - but we still need to hold the mutex
current for the i915_gem_context_lost(). (The issue there is that there
may be an indirect lockdep cycle between cpu_hotplug (i.e. suspend) and
struct_mutex via the stop_machine().) For the moment, enabling last
request tracking for the engine, allows us to do busyness checking and
waiting without requiring the struct_mutex - which is useful in its own
right.

As a side-effect of having a robust means for tracking engine busyness,
we can replace our other busyness heuristic, that of comparing against
the last submitted seqno. For paranoid reasons, we have a semi-ordered
check of that seqno inside the hangchecker, which we can now improve to
an ordered check of the engine's busyness (removing a locked xchg in the
process).

v2: Pass along "bool interruptible" as being unlocked we cannot rely on
i915->mm.interruptible being stable or even under our control.
v3: Replace check Ironlake i915_gpu_busy() with the common precalculated value

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470388464-28458-6-git-send-email-chris@chris-wilson.co.uk

1 files changed, 0 insertions, 18 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 4593a65cae84..322274a239e4 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2227,24 +2227,6 @@ void intel_engine_cleanup(struct intel_engine_cs *engine)
 	engine->i915 = NULL;
 }
 
-int intel_engine_idle(struct intel_engine_cs *engine)
-{
-	struct drm_i915_gem_request *req;
-
-	/* Wait upon the last request to be completed */
-	if (list_empty(&engine->request_list))
-		return 0;
-
-	req = list_entry(engine->request_list.prev,
-			 struct drm_i915_gem_request,
-			 link);
-
-	/* Make sure we do not trigger any retires */
-	return i915_wait_request(req,
-				 req->i915->mm.interruptible,
-				 NULL, NULL);
-}
-
 int intel_ring_alloc_request_extras(struct drm_i915_gem_request *request)
 {
 	int ret;