drm/i915: Move gpu_write_list to per-ring

... to prevent flush processing of an idle (or even absent) ring.

This fixes a regression during suspend from 87acb0a5.

Reported-and-tested-by: Alexey Fisher <bug-track@fisher-privat.net>
Tested-by: Peter Clifton <pcjc2@cam.ac.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 6ab40c6..a05aff0 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -83,6 +83,15 @@
 	struct list_head request_list;
 
 	/**
+	 * List of objects currently pending a GPU write flush.
+	 *
+	 * All elements on this list will belong to either the
+	 * active_list or flushing_list, last_rendering_seqno can
+	 * be used to differentiate between the two elements.
+	 */
+	struct list_head gpu_write_list;
+
+	/**
 	 * Do we have some not yet emitted requests outstanding?
 	 */
 	bool outstanding_lazy_request;