[Intel-gfx] [PATCH 2/2] drm/i915: Disable blt tracking of fbc when not used

[Ben Widawsky]

When not blitting to scanout, we can save some power by not tracking
blits, and more importantly, unnecessarily invalidating lines which we
don't care a bout.

These instructions are explicitly spelled out in the spec, but it is how
I expect it to work. Unfortunately, I do not have power data for this.

Cc: Stéphane Marchesin <marcheu at chromium.org>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index ddd7681..56be8cb 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -296,7 +296,8 @@ static int gen6_ring_fbc_flush(struct intel_ring_buffer *ring)
 			_MASKED_BIT_ENABLE(GEN6_BLITTER_FBC_NOTIFY));
 	intel_ring_advance(ring);
 
-	ring->fbc_dirty = false;
+	/* We'll mark the fbc clean only after the operation has completed so we
+	 * can track when to disable the bit above */
 	return 0;
 }
 
@@ -642,11 +643,13 @@ gen6_add_request(struct intel_ring_buffer *ring)
 	struct drm_device *dev = ring->dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_ring_buffer *useless;
-	int i, ret;
+	int i, ret, extra_dwords = 4;
 
+	if (ring->fbc_dirty && ring->id == BCS)
+		extra_dwords += 4;
 	ret = intel_ring_begin(ring, ((I915_NUM_RINGS-1) *
 				      MBOX_UPDATE_DWORDS) +
-				      4);
+				      extra_dwords);
 	if (ret)
 		return ret;
 #undef MBOX_UPDATE_DWORDS
@@ -661,6 +664,18 @@ gen6_add_request(struct intel_ring_buffer *ring)
 	intel_ring_emit(ring, I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
 	intel_ring_emit(ring, ring->outstanding_lazy_seqno);
 	intel_ring_emit(ring, MI_USER_INTERRUPT);
+
+	if (ring->fbc_dirty && ring->id == BCS) {
+		intel_ring_emit(ring, MI_NOOP);
+		intel_ring_emit(ring, MI_LOAD_REGISTER_IMM(1));
+		intel_ring_emit(ring, GEN6_BLITTER_ECOSKPD);
+		intel_ring_emit(ring,
+				_MASKED_BIT_DISABLE(GEN6_BLITTER_FBC_NOTIFY));
+		__intel_ring_advance(ring);
+
+		ring->fbc_dirty = false;
+	}
+
 	__intel_ring_advance(ring);
 
 	return 0;
-- 
1.8.4.2