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, 4 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 3fecb8f0e041..1f91dc8c4171 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -265,7 +265,7 @@ static int i915_gem_init_seqno(struct drm_i915_private *dev_priv, u32 seqno)
 
 	/* Carefully retire all requests without writing to the rings */
 	for_each_engine(engine, dev_priv) {
-		ret = intel_engine_idle(engine);
+		ret = intel_engine_idle(engine, true);
 		if (ret)
 			return ret;
 	}
@@ -486,7 +486,8 @@ void __i915_add_request(struct drm_i915_gem_request *request,
 	 */
 	request->emitted_jiffies = jiffies;
 	request->previous_seqno = engine->last_submitted_seqno;
-	smp_store_mb(engine->last_submitted_seqno, request->fence.seqno);
+	engine->last_submitted_seqno = request->fence.seqno;
+	i915_gem_active_set(&engine->last_request, request);
 	list_add_tail(&request->link, &engine->request_list);
 	list_add_tail(&request->ring_link, &ring->request_list);
 
@@ -757,7 +758,7 @@ void i915_gem_retire_requests(struct drm_i915_private *dev_priv)
 
 	for_each_engine(engine, dev_priv) {
 		engine_retire_requests(engine);
-		if (list_empty(&engine->request_list))
+		if (!intel_engine_is_active(engine))
 			dev_priv->gt.active_engines &= ~intel_engine_flag(engine);
 	}