drm/i915: Try to fix the messy IVB sprite scaling workaround

We now have a very clear method of disabling LP1+ wartermarks,
and we can actually detect if we actually did disable them, or
if they were already disabled. Use that to clean up the
WaCxSRDisabledForSpriteScaling:ivb handling.

I was hoping to apply the workaround in a way that wouldn't
require a blocking wait, but sadly IVB really does appear to
require LP1+ watermarks to be off for an entire frame before
enabling sprite scaling. Simply disabling LP1+ watermarks
during the previous frame is not enough, no matter how early
in the frame we do it :(

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1401,7 +1401,6 @@ typedef struct drm_i915_private {
 
 	/* overlay */
 	struct intel_overlay *overlay;
-	unsigned int sprite_scaling_enabled;
 
 	/* backlight registers and fields in struct intel_panel */
 	spinlock_t backlight_lock;

drivers/gpu/drm/i915/intel_pm.c

@@ -2426,33 +2426,26 @@ static unsigned int ilk_compute_wm_dirty(struct drm_device *dev,
 	return dirty;
 }
 
-/*
- * The spec says we shouldn't write when we don't need, because every write
- * causes WMs to be re-evaluated, expending some power.
- */
-static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
-				struct hsw_wm_values *results)
+static bool _ilk_disable_lp_wm(struct drm_i915_private *dev_priv,
+			       unsigned int dirty)
 {
-	struct drm_device *dev = dev_priv->dev;
 	struct hsw_wm_values *previous = &dev_priv->wm.hw;
-	unsigned int dirty;
-	uint32_t val;
-
-	dirty = ilk_compute_wm_dirty(dev_priv->dev, previous, results);
-	if (!dirty)
-		return;
+	bool changed = false;
 
 	if (dirty & WM_DIRTY_LP(3) && previous->wm_lp[2] & WM1_LP_SR_EN) {
 		previous->wm_lp[2] &= ~WM1_LP_SR_EN;
 		I915_WRITE(WM3_LP_ILK, previous->wm_lp[2]);
+		changed = true;
 	}
 	if (dirty & WM_DIRTY_LP(2) && previous->wm_lp[1] & WM1_LP_SR_EN) {
 		previous->wm_lp[1] &= ~WM1_LP_SR_EN;
 		I915_WRITE(WM2_LP_ILK, previous->wm_lp[1]);
+		changed = true;
 	}
 	if (dirty & WM_DIRTY_LP(1) && previous->wm_lp[0] & WM1_LP_SR_EN) {
 		previous->wm_lp[0] &= ~WM1_LP_SR_EN;
 		I915_WRITE(WM1_LP_ILK, previous->wm_lp[0]);
+		changed = true;
 	}
 
 	/*
@@ -2460,6 +2453,27 @@ static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
 	 * Doing so could cause underruns.
 	 */
 
+	return changed;
+}
+
+/*
+ * The spec says we shouldn't write when we don't need, because every write
+ * causes WMs to be re-evaluated, expending some power.
+ */
+static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
+				struct hsw_wm_values *results)
+{
+	struct drm_device *dev = dev_priv->dev;
+	struct hsw_wm_values *previous = &dev_priv->wm.hw;
+	unsigned int dirty;
+	uint32_t val;
+
+	dirty = ilk_compute_wm_dirty(dev, previous, results);
+	if (!dirty)
+		return;
+
+	_ilk_disable_lp_wm(dev_priv, dirty);
+
 	if (dirty & WM_DIRTY_PIPE(PIPE_A))
 		I915_WRITE(WM0_PIPEA_ILK, results->wm_pipe[0]);
 	if (dirty & WM_DIRTY_PIPE(PIPE_B))
@@ -2523,6 +2537,13 @@ static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
 	dev_priv->wm.hw = *results;
 }
 
+static bool ilk_disable_lp_wm(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	return _ilk_disable_lp_wm(dev_priv, WM_DIRTY_LP_ALL);
+}
+
 static void haswell_update_wm(struct drm_crtc *crtc)
 {
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
@@ -2572,6 +2593,7 @@ static void haswell_update_sprite_wm(struct drm_plane *plane,
 				     uint32_t sprite_width, int pixel_size,
 				     bool enabled, bool scaled)
 {
+	struct drm_device *dev = plane->dev;
 	struct intel_plane *intel_plane = to_intel_plane(plane);
 
 	intel_plane->wm.enabled = enabled;
@@ -2579,6 +2601,16 @@ static void haswell_update_sprite_wm(struct drm_plane *plane,
 	intel_plane->wm.horiz_pixels = sprite_width;
 	intel_plane->wm.bytes_per_pixel = pixel_size;
 
+	/*
+	 * IVB workaround: must disable low power watermarks for at least
+	 * one frame before enabling scaling.  LP watermarks can be re-enabled
+	 * when scaling is disabled.
+	 *
+	 * WaCxSRDisabledForSpriteScaling:ivb
+	 */
+	if (IS_IVYBRIDGE(dev) && scaled && ilk_disable_lp_wm(dev))
+		intel_wait_for_vblank(dev, intel_plane->pipe);
+
 	haswell_update_wm(crtc);
 }
 

drivers/gpu/drm/i915/intel_sprite.c

@@ -230,7 +230,6 @@ ivb_update_plane(struct drm_plane *plane, struct drm_crtc *crtc,
 	u32 sprctl, sprscale = 0;
 	unsigned long sprsurf_offset, linear_offset;
 	int pixel_size = drm_format_plane_cpp(fb->pixel_format, 0);
-	bool scaling_was_enabled = dev_priv->sprite_scaling_enabled;
 
 	sprctl = I915_READ(SPRCTL(pipe));
 
@@ -291,21 +290,8 @@ ivb_update_plane(struct drm_plane *plane, struct drm_crtc *crtc,
 	crtc_w--;
 	crtc_h--;
 
-	/*
-	 * IVB workaround: must disable low power watermarks for at least
-	 * one frame before enabling scaling.  LP watermarks can be re-enabled
-	 * when scaling is disabled.
-	 */
-	if (crtc_w != src_w || crtc_h != src_h) {
-		dev_priv->sprite_scaling_enabled |= 1 << pipe;
-
-		if (!scaling_was_enabled) {
-			intel_update_watermarks(crtc);
-			intel_wait_for_vblank(dev, pipe);
-		}
+	if (crtc_w != src_w || crtc_h != src_h)
 		sprscale = SPRITE_SCALE_ENABLE | (src_w << 16) | src_h;
-	} else
-		dev_priv->sprite_scaling_enabled &= ~(1 << pipe);
 
 	I915_WRITE(SPRSTRIDE(pipe), fb->pitches[0]);
 	I915_WRITE(SPRPOS(pipe), (crtc_y << 16) | crtc_x);
@@ -332,10 +318,6 @@ ivb_update_plane(struct drm_plane *plane, struct drm_crtc *crtc,
 	I915_MODIFY_DISPBASE(SPRSURF(pipe),
 			     i915_gem_obj_ggtt_offset(obj) + sprsurf_offset);
 	POSTING_READ(SPRSURF(pipe));
-
-	/* potentially re-enable LP watermarks */
-	if (scaling_was_enabled && !dev_priv->sprite_scaling_enabled)
-		intel_update_watermarks(crtc);
 }
 
 static void
@@ -345,7 +327,6 @@ ivb_disable_plane(struct drm_plane *plane, struct drm_crtc *crtc)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_plane *intel_plane = to_intel_plane(plane);
 	int pipe = intel_plane->pipe;
-	bool scaling_was_enabled = dev_priv->sprite_scaling_enabled;
 
 	I915_WRITE(SPRCTL(pipe), I915_READ(SPRCTL(pipe)) & ~SPRITE_ENABLE);
 	/* Can't leave the scaler enabled... */
@@ -355,13 +336,7 @@ ivb_disable_plane(struct drm_plane *plane, struct drm_crtc *crtc)
 	I915_MODIFY_DISPBASE(SPRSURF(pipe), 0);
 	POSTING_READ(SPRSURF(pipe));
 
-	dev_priv->sprite_scaling_enabled &= ~(1 << pipe);
-
 	intel_update_sprite_watermarks(plane, crtc, 0, 0, false, false);
-
-	/* potentially re-enable LP watermarks */
-	if (scaling_was_enabled && !dev_priv->sprite_scaling_enabled)
-		intel_update_watermarks(crtc);
 }
 
 static int