drm/i915/icl: Fail flip if ddb allocated are less than min display buffer needed

ICL require DDB allocation of plane to be more than "minimum display
buffer needed" for each level in order to enable WM level.

This patch implements and consider the same while allocating DDB
and enabling WM.

Changes Since V1:
 - rebase
Changes Since V2:
 - Remove extra parentheses
 - Use FP16.16 only when absolutely necessary (Paulo)
Changes Since V3:
 - Rebase
Changes since v4 (from Paulo):
 - Coding style issue.
Changes since v5 (from Paulo):
 - Do the final checks according to BSpec.

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180130134918.32283-4-paulo.r.zanoni@intel.com

drivers/gpu/drm/i915/intel_pm.c

@@ -4507,6 +4507,7 @@ static int skl_compute_plane_wm(const struct drm_i915_private *dev_priv,
 	struct intel_atomic_state *state =
 		to_intel_atomic_state(cstate->base.state);
 	bool apply_memory_bw_wa = skl_needs_memory_bw_wa(state);
+	uint32_t min_disp_buf_needed;
 
 	if (latency == 0 ||
 	    !intel_wm_plane_visible(cstate, intel_pstate)) {
@@ -4565,7 +4566,31 @@ static int skl_compute_plane_wm(const struct drm_i915_private *dev_priv,
 		}
 	}
 
-	if (res_blocks >= ddb_allocation || res_lines > 31) {
+	if (INTEL_GEN(dev_priv) >= 11) {
+		if (wp->y_tiled) {
+			uint32_t extra_lines;
+			uint_fixed_16_16_t fp_min_disp_buf_needed;
+
+			if (res_lines % wp->y_min_scanlines == 0)
+				extra_lines = wp->y_min_scanlines;
+			else
+				extra_lines = wp->y_min_scanlines * 2 -
+					      res_lines % wp->y_min_scanlines;
+
+			fp_min_disp_buf_needed = mul_u32_fixed16(res_lines +
+						extra_lines,
+						wp->plane_blocks_per_line);
+			min_disp_buf_needed = fixed16_to_u32_round_up(
+						fp_min_disp_buf_needed);
+		} else {
+			min_disp_buf_needed = DIV_ROUND_UP(res_blocks * 11, 10);
+		}
+	} else {
+		min_disp_buf_needed = res_blocks;
+	}
+
+	if (res_blocks >= ddb_allocation || res_lines > 31 ||
+	    min_disp_buf_needed >= ddb_allocation) {
 		*enabled = false;
 
 		/*