drm/i915: add flags to i915_ring_stop

Piglit runner and QA are both looking at the dmesg for
DRM_ERRORs with test cases. Add a flag to control those
when we they are expected from related test cases.

Also add flag to control if contexts should be banned
that introduced the hang. Hangcheck is timer based and
preventing bans by adding sleeps to testcases makes
testing slower.

v2: intel_ring_stopped(), readable comment (Chris)
v3: keep compatibility (Daniel)

References: https://bugs.freedesktop.org/show_bug.cgi?id=75876
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 3d76ce1..eb3dd26 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -41,12 +41,16 @@
 	return space;
 }
 
-void __intel_ring_advance(struct intel_ring_buffer *ring)
+static bool intel_ring_stopped(struct intel_ring_buffer *ring)
 {
 	struct drm_i915_private *dev_priv = ring->dev->dev_private;
+	return dev_priv->gpu_error.stop_rings & intel_ring_flag(ring);
+}
 
+void __intel_ring_advance(struct intel_ring_buffer *ring)
+{
 	ring->tail &= ring->size - 1;
-	if (dev_priv->gpu_error.stop_rings & intel_ring_flag(ring))
+	if (intel_ring_stopped(ring))
 		return;
 	ring->write_tail(ring, ring->tail);
 }