drm/i915: FBC flush nuke for BDW

According to spec FBC on BDW and HSW are identical without any gaps.
So let's copy the nuke and let FBC really start compressing stuff.

Without this patch we can verify with false color that nothing is being
compressed. With the nuke in place and false color it is possible
to see false color debugs.

Unfortunatelly on some rings like BCS on BDW we have to avoid Bits 22:18 on
LRIs due to a high risk of hung. So, when using Blt ring for frontbuffer rend
cache would never been cleaned and FBC would stop compressing buffer.
One alternative is to cache clean on software frontbuffer tracking.

v2: Fix rebase conflict.
v3: Do not clean cache on BCS ring. Instead use sw frontbuffer tracking.
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -2772,6 +2772,7 @@ extern void intel_modeset_setup_hw_state(struct drm_device *dev,
 extern void i915_redisable_vga(struct drm_device *dev);
 extern void i915_redisable_vga_power_on(struct drm_device *dev);
 extern bool intel_fbc_enabled(struct drm_device *dev);
+extern void gen8_fbc_sw_flush(struct drm_device *dev, u32 value);
 extern void intel_disable_fbc(struct drm_device *dev);
 extern bool ironlake_set_drps(struct drm_device *dev, u8 val);
 extern void intel_init_pch_refclk(struct drm_device *dev);

drivers/gpu/drm/i915/intel_display.c

@@ -9082,6 +9082,9 @@ void intel_frontbuffer_flush(struct drm_device *dev,
 	intel_mark_fb_busy(dev, frontbuffer_bits, NULL);
 
 	intel_edp_psr_flush(dev, frontbuffer_bits);
+
+	if (IS_GEN8(dev))
+		gen8_fbc_sw_flush(dev, FBC_REND_CACHE_CLEAN);
 }
 
 /**

drivers/gpu/drm/i915/intel_pm.c

@@ -345,6 +345,16 @@ bool intel_fbc_enabled(struct drm_device *dev)
 	return dev_priv->display.fbc_enabled(dev);
 }
 
+void gen8_fbc_sw_flush(struct drm_device *dev, u32 value)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (!IS_GEN8(dev))
+		return;
+
+	I915_WRITE(MSG_FBC_REND_STATE, value);
+}
+
 static void intel_fbc_work_fn(struct work_struct *__work)
 {
 	struct intel_fbc_work *work =

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -444,7 +444,14 @@ gen8_render_ring_flush(struct intel_engine_cs *ring,
 			return ret;
 	}
 
-	return gen8_emit_pipe_control(ring, flags, scratch_addr);
+	ret = gen8_emit_pipe_control(ring, flags, scratch_addr);
+	if (ret)
+		return ret;
+
+	if (!invalidate_domains && flush_domains)
+		return gen7_ring_fbc_flush(ring, FBC_REND_NUKE);
+
+	return 0;
 }
 
 static void ring_write_tail(struct intel_engine_cs *ring,