drm/i915/gen10: Calculate and enable transition WM

GEN > 9 require transition WM to be programmed if IPC is enabled.
This patch calculates & enable transition WM for supported platforms.
If transition WM is enabled, Plane read requests are sent at high
priority until filling above the transition watermark, then the
requests are sent at lower priority until dropping below the level-0 WM.
The lower priority requests allow other memory clients to have better
memory access.

transition minimum is the minimum amount needed for trans_wm to work to
ensure  the demote does not happen before enough data has been read to
meet the level 0 watermark requirements.

transition amount is configurable value. Higher values will
tend to cause longer periods of high priority reads followed by longer
periods of lower priority reads. Tuning to lower values will tend to
cause shorter periods of high and lower priority reads.

Keeping transition amount to 10 in this patch, as suggested by HW team.

Changes since V1:
 - Address review comments from Maarten
Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170817134529.2839-4-mahesh1.kumar@intel.com

drivers/gpu/drm/i915/intel_pm.c

@@ -4630,12 +4630,56 @@ skl_compute_linetime_wm(struct intel_crtc_state *cstate)
 }
 
 static void skl_compute_transition_wm(struct intel_crtc_state *cstate,
+				      struct skl_wm_params *wp,
+				      struct skl_wm_level *wm_l0,
+				      uint16_t ddb_allocation,
 				      struct skl_wm_level *trans_wm /* out */)
 {
+	struct drm_device *dev = cstate->base.crtc->dev;
+	const struct drm_i915_private *dev_priv = to_i915(dev);
+	uint16_t trans_min, trans_y_tile_min;
+	const uint16_t trans_amount = 10; /* This is configurable amount */
+	uint16_t trans_offset_b, res_blocks;
+
 	if (!cstate->base.active)
+		goto exit;
+
+	/* Transition WM are not recommended by HW team for GEN9 */
+	if (INTEL_GEN(dev_priv) <= 9)
+		goto exit;
+
+	/* Transition WM don't make any sense if ipc is disabled */
+	if (!dev_priv->ipc_enabled)
+		goto exit;
+
+	if (INTEL_GEN(dev_priv) >= 10)
+		trans_min = 4;
+
+	trans_offset_b = trans_min + trans_amount;
+
+	if (wp->y_tiled) {
+		trans_y_tile_min = (uint16_t) mul_round_up_u32_fixed16(2,
+							wp->y_tile_minimum);
+		res_blocks = max(wm_l0->plane_res_b, trans_y_tile_min) +
+				trans_offset_b;
+	} else {
+		res_blocks = wm_l0->plane_res_b + trans_offset_b;
+
+		/* WA BUG:1938466 add one block for non y-tile planes */
+		if (IS_CNL_REVID(dev_priv, CNL_REVID_A0, CNL_REVID_A0))
+			res_blocks += 1;
+
+	}
+
+	res_blocks += 1;
+
+	if (res_blocks < ddb_allocation) {
+		trans_wm->plane_res_b = res_blocks;
+		trans_wm->plane_en = true;
 		return;
+	}
 
-	/* Until we know more, just disable transition WMs */
+exit:
 	trans_wm->plane_en = false;
 }
 
@@ -4662,8 +4706,11 @@ static int skl_build_pipe_wm(struct intel_crtc_state *cstate,
 						to_intel_plane_state(pstate);
 		enum plane_id plane_id = to_intel_plane(plane)->id;
 		struct skl_wm_params wm_params;
+		enum pipe pipe = to_intel_crtc(cstate->base.crtc)->pipe;
+		uint16_t ddb_blocks;
 
 		wm = &pipe_wm->planes[plane_id];
+		ddb_blocks = skl_ddb_entry_size(&ddb->plane[pipe][plane_id]);
 		memset(&wm_params, 0, sizeof(struct skl_wm_params));
 
 		ret = skl_compute_plane_wm_params(dev_priv, cstate,
@@ -4675,7 +4722,8 @@ static int skl_build_pipe_wm(struct intel_crtc_state *cstate,
 					    intel_pstate, &wm_params, wm);
 		if (ret)
 			return ret;
-		skl_compute_transition_wm(cstate, &wm->trans_wm);
+		skl_compute_transition_wm(cstate, &wm_params, &wm->wm[0],
+					  ddb_blocks, &wm->trans_wm);
 	}
 	pipe_wm->linetime = skl_compute_linetime_wm(cstate);