[PATCH v2] drm/i915: set scanout buffer as uncached on Sandybridge

[Zhenyu Wang <zhenyuw@linux.intel.com>]

Display engine on Sandybridge is not coherent with LLC, so
try to always bind display buffer as uncached on Sandybridge.
Old AGP_USER_MEMORY is bound as uncached by default, as Sandybridge
buffer would try to live in LLC with CPU as possible, so it uses
new flag AGP_USER_UNCACHED_MEMORY for uncached binding.

This is based on review and comment from Chris Wilson.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h      |    1 +
 drivers/gpu/drm/i915/i915_gem.c      |   20 ++++++++++++++++++++
 drivers/gpu/drm/i915/intel_display.c |   10 ++++++++++
 3 files changed, 31 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 2c2c19b..5948e05 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1025,6 +1025,7 @@ void i915_gem_object_unpin(struct drm_gem_object *obj);
 int i915_gem_object_unbind(struct drm_gem_object *obj);
 void i915_gem_release_mmap(struct drm_gem_object *obj);
 void i915_gem_lastclose(struct drm_device *dev);
+int i915_gem_object_enable_scanout(struct drm_gem_object *obj);
 
 /**
  * Returns true if seq1 is later than seq2.
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 8eb8453..78f6789 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4028,6 +4028,26 @@ i915_gem_execbuffer2(struct drm_device *dev, void *data,
 }
 
 int
+i915_gem_object_enable_scanout(struct drm_gem_object *obj)
+{
+	struct drm_device *dev = obj->dev;
+	struct drm_i915_gem_object *obj_priv = to_intel_bo(obj);
+	int type = IS_GEN6(dev) ? AGP_USER_UNCACHED_MEMORY : AGP_USER_MEMORY;
+
+	if (obj_priv->agp_type == type)
+		return 0;
+
+	if (obj_priv->gtt_space) {
+		int ret = i915_gem_object_unbind(obj);
+		if (ret)
+			return ret;
+	}
+
+	obj_priv->agp_type = type;
+	return 0;
+}
+
+int
 i915_gem_object_pin(struct drm_gem_object *obj, uint32_t alignment)
 {
 	struct drm_device *dev = obj->dev;
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 990f065..a413db6 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -1461,6 +1461,10 @@ intel_pin_and_fence_fb_obj(struct drm_device *dev,
 		BUG();
 	}
 
+	ret = i915_gem_object_enable_scanout(obj);
+	if (ret)
+		return ret;
+
 	ret = i915_gem_object_pin(obj, alignment);
 	if (ret)
 		return ret;
@@ -5482,6 +5486,12 @@ intel_user_framebuffer_create(struct drm_device *dev,
 	if (!intel_fb)
 		return ERR_PTR(-ENOMEM);
 
+	ret = i915_gem_object_enable_scanout(obj);
+	if (ret) {
+		kfree(intel_fb);
+		return ERR_PTR(ret);
+	}
+
 	ret = intel_framebuffer_init(dev, intel_fb,
 				     mode_cmd, obj);
 	if (ret) {
-- 
1.7.1