drm/i915: Improve watermark dirtyness checks

Currently hsw_write_vm_values() may write to certain watermark
registers needlessly. For instance if only, say, LP3 changes,
the current code will again disable all LP1+ watermarks even
though only LP3 needs to be reconfigured.

Add an easy to read function that will compute the dirtyness of the
watermarks, and use that information to further optimize the watermark
programming.

v2: Disable LP1+ watermarks around changing LP0 watermarks for Paulo
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -2776,6 +2776,66 @@ static struct intel_pipe_wm *hsw_find_best_result(struct drm_device *dev,
 	}
 }
 
+/* dirty bits used to track which watermarks need changes */
+#define WM_DIRTY_PIPE(pipe) (1 << (pipe))
+#define WM_DIRTY_LINETIME(pipe) (1 << (8 + (pipe)))
+#define WM_DIRTY_LP(wm_lp) (1 << (15 + (wm_lp)))
+#define WM_DIRTY_LP_ALL (WM_DIRTY_LP(1) | WM_DIRTY_LP(2) | WM_DIRTY_LP(3))
+#define WM_DIRTY_FBC (1 << 24)
+#define WM_DIRTY_DDB (1 << 25)
+
+static unsigned int ilk_compute_wm_dirty(struct drm_device *dev,
+					 const struct hsw_wm_values *old,
+					 const struct hsw_wm_values *new)
+{
+	unsigned int dirty = 0;
+	enum pipe pipe;
+	int wm_lp;
+
+	for_each_pipe(pipe) {
+		if (old->wm_linetime[pipe] != new->wm_linetime[pipe]) {
+			dirty |= WM_DIRTY_LINETIME(pipe);
+			/* Must disable LP1+ watermarks too */
+			dirty |= WM_DIRTY_LP_ALL;
+		}
+
+		if (old->wm_pipe[pipe] != new->wm_pipe[pipe]) {
+			dirty |= WM_DIRTY_PIPE(pipe);
+			/* Must disable LP1+ watermarks too */
+			dirty |= WM_DIRTY_LP_ALL;
+		}
+	}
+
+	if (old->enable_fbc_wm != new->enable_fbc_wm) {
+		dirty |= WM_DIRTY_FBC;
+		/* Must disable LP1+ watermarks too */
+		dirty |= WM_DIRTY_LP_ALL;
+	}
+
+	if (old->partitioning != new->partitioning) {
+		dirty |= WM_DIRTY_DDB;
+		/* Must disable LP1+ watermarks too */
+		dirty |= WM_DIRTY_LP_ALL;
+	}
+
+	/* LP1+ watermarks already deemed dirty, no need to continue */
+	if (dirty & WM_DIRTY_LP_ALL)
+		return dirty;
+
+	/* Find the lowest numbered LP1+ watermark in need of an update... */
+	for (wm_lp = 1; wm_lp <= 3; wm_lp++) {
+		if (old->wm_lp[wm_lp - 1] != new->wm_lp[wm_lp - 1] ||
+		    old->wm_lp_spr[wm_lp - 1] != new->wm_lp_spr[wm_lp - 1])
+			break;
+	}
+
+	/* ...and mark it and all higher numbered LP1+ watermarks as dirty */
+	for (; wm_lp <= 3; wm_lp++)
+		dirty |= WM_DIRTY_LP(wm_lp);
+
+	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.
@@ -2784,6 +2844,7 @@ static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
 				struct hsw_wm_values *results)
 {
 	struct hsw_wm_values previous;
+	unsigned int dirty;
 	uint32_t val;
 
 	previous.wm_pipe[0] = I915_READ(WM0_PIPEA_ILK);
@@ -2804,31 +2865,32 @@ static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
 
 	previous.enable_fbc_wm = !(I915_READ(DISP_ARB_CTL) & DISP_FBC_WM_DIS);
 
-	if (memcmp(results, &previous, sizeof(*results)) == 0)
+	dirty = ilk_compute_wm_dirty(dev_priv->dev, &previous, results);
+	if (!dirty)
 		return;
 
-	if (previous.wm_lp[2] != 0)
+	if (dirty & WM_DIRTY_LP(3) && previous.wm_lp[2] != 0)
 		I915_WRITE(WM3_LP_ILK, 0);
-	if (previous.wm_lp[1] != 0)
+	if (dirty & WM_DIRTY_LP(2) && previous.wm_lp[1] != 0)
 		I915_WRITE(WM2_LP_ILK, 0);
-	if (previous.wm_lp[0] != 0)
+	if (dirty & WM_DIRTY_LP(1) && previous.wm_lp[0] != 0)
 		I915_WRITE(WM1_LP_ILK, 0);
 
-	if (previous.wm_pipe[0] != results->wm_pipe[0])
+	if (dirty & WM_DIRTY_PIPE(PIPE_A))
 		I915_WRITE(WM0_PIPEA_ILK, results->wm_pipe[0]);
-	if (previous.wm_pipe[1] != results->wm_pipe[1])
+	if (dirty & WM_DIRTY_PIPE(PIPE_B))
 		I915_WRITE(WM0_PIPEB_ILK, results->wm_pipe[1]);
-	if (previous.wm_pipe[2] != results->wm_pipe[2])
+	if (dirty & WM_DIRTY_PIPE(PIPE_C))
 		I915_WRITE(WM0_PIPEC_IVB, results->wm_pipe[2]);
 
-	if (previous.wm_linetime[0] != results->wm_linetime[0])
+	if (dirty & WM_DIRTY_LINETIME(PIPE_A))
 		I915_WRITE(PIPE_WM_LINETIME(PIPE_A), results->wm_linetime[0]);
-	if (previous.wm_linetime[1] != results->wm_linetime[1])
+	if (dirty & WM_DIRTY_LINETIME(PIPE_B))
 		I915_WRITE(PIPE_WM_LINETIME(PIPE_B), results->wm_linetime[1]);
-	if (previous.wm_linetime[2] != results->wm_linetime[2])
+	if (dirty & WM_DIRTY_LINETIME(PIPE_C))
 		I915_WRITE(PIPE_WM_LINETIME(PIPE_C), results->wm_linetime[2]);
 
-	if (previous.partitioning != results->partitioning) {
+	if (dirty & WM_DIRTY_DDB) {
 		val = I915_READ(WM_MISC);
 		if (results->partitioning == INTEL_DDB_PART_1_2)
 			val &= ~WM_MISC_DATA_PARTITION_5_6;
@@ -2837,7 +2899,7 @@ static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
 		I915_WRITE(WM_MISC, val);
 	}
 
-	if (previous.enable_fbc_wm != results->enable_fbc_wm) {
+	if (dirty & WM_DIRTY_FBC) {
 		val = I915_READ(DISP_ARB_CTL);
 		if (results->enable_fbc_wm)
 			val &= ~DISP_FBC_WM_DIS;
@@ -2846,18 +2908,18 @@ static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
 		I915_WRITE(DISP_ARB_CTL, val);
 	}
 
-	if (previous.wm_lp_spr[0] != results->wm_lp_spr[0])
+	if (dirty & WM_DIRTY_LP(1) && previous.wm_lp_spr[0] != results->wm_lp_spr[0])
 		I915_WRITE(WM1S_LP_ILK, results->wm_lp_spr[0]);
-	if (previous.wm_lp_spr[1] != results->wm_lp_spr[1])
+	if (dirty & WM_DIRTY_LP(2) && previous.wm_lp_spr[1] != results->wm_lp_spr[1])
 		I915_WRITE(WM2S_LP_IVB, results->wm_lp_spr[1]);
-	if (previous.wm_lp_spr[2] != results->wm_lp_spr[2])
+	if (dirty & WM_DIRTY_LP(3) && previous.wm_lp_spr[2] != results->wm_lp_spr[2])
 		I915_WRITE(WM3S_LP_IVB, results->wm_lp_spr[2]);
 
-	if (results->wm_lp[0] != 0)
+	if (dirty & WM_DIRTY_LP(1) && results->wm_lp[0] != 0)
 		I915_WRITE(WM1_LP_ILK, results->wm_lp[0]);
-	if (results->wm_lp[1] != 0)
+	if (dirty & WM_DIRTY_LP(2) && results->wm_lp[1] != 0)
 		I915_WRITE(WM2_LP_ILK, results->wm_lp[1]);
-	if (results->wm_lp[2] != 0)
+	if (dirty & WM_DIRTY_LP(3) && results->wm_lp[2] != 0)
 		I915_WRITE(WM3_LP_ILK, results->wm_lp[2]);
 
 	dev_priv->wm.hw = *results;