drm/i915: track sprite coverage and disable primary plane if possible

To save power when the sprite is full screen, we can disable the primary
plane on the same pipe.  Track the sprite status and enable/disable the
primary opportunistically.

v2: remove primary plane enable/disable hooks; they're identical

Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>
diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
index c77717d..6994e06 100644
--- a/drivers/gpu/drm/i915/intel_sprite.c
+++ b/drivers/gpu/drm/i915/intel_sprite.c
@@ -256,6 +256,28 @@
 	POSTING_READ(DVSSURF(pipe));
 }
 
+static void
+intel_enable_primary(struct drm_crtc *crtc)
+{
+	struct drm_device *dev = crtc->dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+	int reg = DSPCNTR(intel_crtc->plane);
+
+	I915_WRITE(reg, I915_READ(reg) | DISPLAY_PLANE_ENABLE);
+}
+
+static void
+intel_disable_primary(struct drm_crtc *crtc)
+{
+	struct drm_device *dev = crtc->dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+	int reg = DSPCNTR(intel_crtc->plane);
+
+	I915_WRITE(reg, I915_READ(reg) & ~DISPLAY_PLANE_ENABLE);
+}
+
 static int
 intel_update_plane(struct drm_plane *plane, struct drm_crtc *crtc,
 		   struct drm_framebuffer *fb, int crtc_x, int crtc_y,
@@ -342,9 +364,23 @@
 
 	intel_plane->obj = obj;
 
+	/*
+	 * Be sure to re-enable the primary before the sprite is no longer
+	 * covering it fully.
+	 */
+	if (!disable_primary && intel_plane->primary_disabled) {
+		intel_enable_primary(crtc);
+		intel_plane->primary_disabled = false;
+	}
+
 	intel_plane->update_plane(plane, fb, obj, crtc_x, crtc_y,
 				  crtc_w, crtc_h, x, y, src_w, src_h);
 
+	if (disable_primary) {
+		intel_disable_primary(crtc);
+		intel_plane->primary_disabled = true;
+	}
+
 	/* Unpin old obj after new one is active to avoid ugliness */
 	if (old_obj) {
 		/*
@@ -374,6 +410,11 @@
 	struct intel_plane *intel_plane = to_intel_plane(plane);
 	int ret = 0;
 
+	if (intel_plane->primary_disabled) {
+		intel_enable_primary(plane->crtc);
+		intel_plane->primary_disabled = false;
+	}
+
 	intel_plane->disable_plane(plane);
 
 	if (!intel_plane->obj)