drm/i915/bdw: Add a context and an engine pointers to the ringbuffer

Any given ringbuffer is unequivocally tied to one context and one engine.
By setting the appropriate pointers to them, the ringbuffer struct holds
all the infromation you might need to submit a workload for processing,
Execlists style.

v2: Drop ring->ctx since that looks terribly ill-defined for legacy
ringbuffer submission.

Signed-off-by: Oscar Mateo <oscar.mateo@intel.com> (v1)
Acked-by: Damien Lespiau <damien.lespiau@intel.com> (v2)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 0c80bb1..8f2d14d 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -134,6 +134,7 @@
 		return ret;
 	}
 
+	ringbuf->ring = ring;
 	ringbuf->size = 32 * PAGE_SIZE;
 	ringbuf->effective_size = ringbuf->size;
 	ringbuf->head = 0;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 0646520..c35f956 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1594,6 +1594,7 @@
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
 	ringbuf->size = 32 * PAGE_SIZE;
+	ringbuf->ring = ring;
 	memset(ring->semaphore.sync_seqno, 0, sizeof(ring->semaphore.sync_seqno));
 
 	init_waitqueue_head(&ring->irq_queue);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 669cc75..fe9d9d9 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -90,6 +90,8 @@
 	struct drm_i915_gem_object *obj;
 	void __iomem *virtual_start;
 
+	struct intel_engine_cs *ring;
+
 	u32 head;
 	u32 tail;
 	int space;