drm/i915: Extract skl_wm_latency()

Extract the skl+ wm latency determination into a small helper
so that everyone has the same idea what the latency should be.

This introduces a slight functional change in that
skl_cursor_allocation() will now start to account for the
extra 4 usec that the kbk/cfl/cml IPC w/a adds.

v2: Rebase
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230301162449.26672-2-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/skl_watermark.c

@@ -704,6 +704,28 @@ static void skl_compute_plane_wm(const struct intel_crtc_state *crtc_state,
 				 const struct skl_wm_level *result_prev,
 				 struct skl_wm_level *result /* out */);
 
+static unsigned int skl_wm_latency(struct drm_i915_private *i915, int level,
+				   const struct skl_wm_params *wp)
+{
+	unsigned int latency = i915->display.wm.skl_latency[level];
+
+	if (latency == 0)
+		return 0;
+
+	/*
+	 * WaIncreaseLatencyIPCEnabled: kbl,cfl
+	 * Display WA #1141: kbl,cfl
+	 */
+	if ((IS_KABYLAKE(i915) || IS_COFFEELAKE(i915) || IS_COMETLAKE(i915)) &&
+	    skl_watermark_ipc_enabled(i915))
+		latency += 4;
+
+	if (skl_needs_memory_bw_wa(i915) && wp->x_tiled)
+		latency += 15;
+
+	return latency;
+}
+
 static unsigned int
 skl_cursor_allocation(const struct intel_crtc_state *crtc_state,
 		      int num_active)
@@ -723,7 +745,7 @@ skl_cursor_allocation(const struct intel_crtc_state *crtc_state,
 	drm_WARN_ON(&i915->drm, ret);
 
 	for (level = 0; level < i915->display.wm.num_levels; level++) {
-		unsigned int latency = i915->display.wm.skl_latency[level];
+		unsigned int latency = skl_wm_latency(i915, level, &wp);
 
 		skl_compute_plane_wm(crtc_state, plane, level, latency, &wp, &wm, &wm);
 		if (wm.min_ddb_alloc == U16_MAX)
@@ -1839,17 +1861,6 @@ static void skl_compute_plane_wm(const struct intel_crtc_state *crtc_state,
 		return;
 	}
 
-	/*
-	 * WaIncreaseLatencyIPCEnabled: kbl,cfl
-	 * Display WA #1141: kbl,cfl
-	 */
-	if ((IS_KABYLAKE(i915) || IS_COFFEELAKE(i915) || IS_COMETLAKE(i915)) &&
-	    skl_watermark_ipc_enabled(i915))
-		latency += 4;
-
-	if (skl_needs_memory_bw_wa(i915) && wp->x_tiled)
-		latency += 15;
-
 	method1 = skl_wm_method1(i915, wp->plane_pixel_rate,
 				 wp->cpp, latency, wp->dbuf_block_size);
 	method2 = skl_wm_method2(wp->plane_pixel_rate,
@@ -1976,7 +1987,7 @@ skl_compute_wm_levels(const struct intel_crtc_state *crtc_state,
 
 	for (level = 0; level < i915->display.wm.num_levels; level++) {
 		struct skl_wm_level *result = &levels[level];
-		unsigned int latency = i915->display.wm.skl_latency[level];
+		unsigned int latency = skl_wm_latency(i915, level, wm_params);
 
 		skl_compute_plane_wm(crtc_state, plane, level, latency,
 				     wm_params, result_prev, result);
@@ -1996,7 +2007,8 @@ static void tgl_compute_sagv_wm(const struct intel_crtc_state *crtc_state,
 	unsigned int latency = 0;
 
 	if (i915->display.sagv.block_time_us)
-		latency = i915->display.sagv.block_time_us + i915->display.wm.skl_latency[0];
+		latency = i915->display.sagv.block_time_us +
+			skl_wm_latency(i915, 0, wm_params);
 
 	skl_compute_plane_wm(crtc_state, plane, 0, latency,
 			     wm_params, &levels[0],