[PATCH 9/9] drm/i915/gen10: Calculate and enable transition WM

[Mahesh Kumar]

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 0 in this patch.

Signed-off-by: Mahesh Kumar <mahesh1.kumar at intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 51 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 55f9e1ae0a94..4bbe242643cf 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -4197,6 +4197,15 @@ skl_enable_plane_wm_levels(const struct drm_i915_private *dev_priv,
 			level_wm->plane_en = true;
 		}
 	}
+
+	/*
+	 * Unsupported GEN will have plane_res_b = 0 & transition WM for
+	 * them will get disabled here.
+	 */
+	if (wm->trans_wm.plane_res_b && wm->trans_wm.plane_res_b < plane_ddb)
+		wm->trans_wm.plane_en = true;
+	else
+		wm->trans_wm.plane_en = false;
 }
 
 static int
@@ -4640,13 +4649,48 @@ 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,
 				      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;
+	uint16_t trans_amount = 0; /* This is configurable amount */
+	uint16_t trans_offset_b, res_blocks;
+
 	if (!cstate->base.active)
 		return;
 
-	/* Until we know more, just disable transition WMs */
-	trans_wm->plane_en = false;
+	/* Transition WM are not recommended by HW team for GEN9 */
+	if (INTEL_GEN(dev_priv) <= 9)
+		return;
+
+	/* Transition WM don't have any impact if ipc is disabled */
+	if (!dev_priv->ipc_enabled)
+		return;
+
+	if (INTEL_GEN(dev_priv) >= 10)
+		trans_min = 4;
+
+	trans_offset_b = trans_min + trans_amount;
+	trans_y_tile_min = (uint16_t) mul_round_up_u32_fixed16(2,
+							wp->y_tile_minimum);
+
+	if (wp->y_tiled) {
+		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;
+	}
+
+	res_blocks += 1;
+
+	/* WA BUG:1938466 add one block for non y-tile planes */
+	if (!wp->y_tiled && IS_CNL_REVID(dev_priv, CNL_REVID_A0, CNL_REVID_A0))
+		res_blocks += 1;
+
+	trans_wm->plane_res_b = res_blocks;
 }
 
 static int skl_build_pipe_wm(struct intel_crtc_state *cstate,
@@ -4685,7 +4729,8 @@ static int skl_build_pipe_wm(struct intel_crtc_state *cstate,
 					    &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],
+					  &wm->trans_wm);
 	}
 	pipe_wm->linetime = skl_compute_linetime_wm(cstate);
 
-- 
2.13.0