[Intel-gfx] [PATCH 1/2] drm/i915: Fix fbc + rc6 combination on SNB

[Ben Widawsky]

On Sandybridge we must set the "PPGTT Render Target Base Address Valid
for FBC" bit as noted in the programming guide. We did this at clock
gating init. Thisbit is not saved and restored with RC6 power context,
so the resetting it at ring flush should fix that.

The effect of not doing this should be corruption, and not a hang - as
has so often been the case.

Note that we should actually clear this bit as well when not blitting to
the scanout (using the blitter for other things), or else all operations

Cc: Stéphane Marchesin <marcheu at chromium.org>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/intel_pm.c         |  2 --
 drivers/gpu/drm/i915/intel_ringbuffer.c | 25 +++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index ca9a778..67f460b 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -193,8 +193,6 @@ static void sandybridge_blit_fbc_update(struct drm_device *dev)
 	/* Make sure blitter notifies FBC of writes */
 	gen6_gt_force_wake_get(dev_priv);
 	blt_ecoskpd = I915_READ(GEN6_BLITTER_ECOSKPD);
-	blt_ecoskpd |= GEN6_BLITTER_FBC_NOTIFY <<
-		GEN6_BLITTER_LOCK_SHIFT;
 	I915_WRITE(GEN6_BLITTER_ECOSKPD, blt_ecoskpd);
 	blt_ecoskpd |= GEN6_BLITTER_FBC_NOTIFY;
 	I915_WRITE(GEN6_BLITTER_ECOSKPD, blt_ecoskpd);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 2dec134..ddd7681 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -278,6 +278,28 @@ gen7_render_ring_cs_stall_wa(struct intel_ring_buffer *ring)
 	return 0;
 }
 
+static int gen6_ring_fbc_flush(struct intel_ring_buffer *ring)
+{
+	int ret;
+
+	if (!ring->fbc_dirty)
+		return 0;
+
+	ret = intel_ring_begin(ring, 4);
+	if (ret)
+		return ret;
+
+	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_ENABLE(GEN6_BLITTER_FBC_NOTIFY));
+	intel_ring_advance(ring);
+
+	ring->fbc_dirty = false;
+	return 0;
+}
+
 static int gen7_ring_fbc_flush(struct intel_ring_buffer *ring, u32 value)
 {
 	int ret;
@@ -1712,6 +1734,9 @@ static int gen6_ring_flush(struct intel_ring_buffer *ring,
 	intel_ring_emit(ring, MI_NOOP);
 	intel_ring_advance(ring);
 
+	if (IS_GEN6(dev) && flush)
+		return gen6_ring_fbc_flush(ring);
+
 	if (IS_GEN7(dev) && flush)
 		return gen7_ring_fbc_flush(ring, FBC_REND_CACHE_CLEAN);
 
-- 
1.8.4.2