[Intel-gfx] [PATCH 5/5] drm/i915: Reject wm levels that exceed vblank time

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

The pipe needs a certain amount of time during vblank to prefill
sufficiently. If the vblank is too short the relevant watermark
level must be disabled.

Start implementing the necessary calculations to check this.
Scaler and DSC prefill are left out for now as handling those
is not entirely trivial.

Also the PSR latency reporting override chicken bits would
need to be correctly configured based on the results of these
calculations. Just add some FIXMEs for now.

TODO: bspec isn't exactly crystal clear in its explanations
      so quite a few open questions remain...

Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/display/skl_watermark.c | 98 +++++++++++++++++++-
 1 file changed, 96 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
index 65c746d018b5..495d85b866e0 100644
--- a/drivers/gpu/drm/i915/display/skl_watermark.c
+++ b/drivers/gpu/drm/i915/display/skl_watermark.c
@@ -8,6 +8,7 @@
 #include "intel_atomic.h"
 #include "intel_atomic_plane.h"
 #include "intel_bw.h"
+#include "intel_crtc.h"
 #include "intel_de.h"
 #include "intel_display.h"
 #include "intel_display_power.h"
@@ -720,7 +721,7 @@ static unsigned int skl_wm_latency(struct drm_i915_private *i915, int level,
 	    skl_watermark_ipc_enabled(i915))
 		latency += 4;
 
-	if (skl_needs_memory_bw_wa(i915) && wp->x_tiled)
+	if (skl_needs_memory_bw_wa(i915) && wp && wp->x_tiled)
 		latency += 15;
 
 	return latency;
@@ -2195,6 +2196,99 @@ static int icl_build_plane_wm(struct intel_crtc_state *crtc_state,
 	return 0;
 }
 
+static bool
+skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
+			int wm0_lines, int latency)
+{
+	const struct drm_display_mode *adjusted_mode =
+		&crtc_state->hw.adjusted_mode;
+
+	/* FIXME missing scaler and DSC pre-fill time */
+	return crtc_state->framestart_delay +
+		intel_usecs_to_scanlines(adjusted_mode, latency) +
+		wm0_lines >
+		adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
+}
+
+static int skl_max_wm0_lines(const struct intel_crtc_state *crtc_state)
+{
+	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
+	enum plane_id plane_id;
+	int wm0_lines = 0;
+
+	for_each_plane_id_on_crtc(crtc, plane_id) {
+		const struct skl_plane_wm *wm = &crtc_state->wm.skl.optimal.planes[plane_id];
+
+		/* FIXME what about !skl_wm_has_lines() platforms? */
+		wm0_lines = max_t(int, wm0_lines, wm->wm[0].lines);
+	}
+
+	return wm0_lines;
+}
+
+static int skl_max_wm_level_for_vblank(struct intel_crtc_state *crtc_state)
+{
+	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
+	struct drm_i915_private *i915 = to_i915(crtc->base.dev);
+	int wm0_lines = skl_max_wm0_lines(crtc_state);
+	int level;
+
+	for (level = ilk_wm_max_level(i915); level >= 0; level--) {
+		int latency;
+
+		/*
+		 * FIXME is it correct to use 0 latency for wm0 here?
+		 * FIXME should we care about the latency w/a's?
+		 * FIXME what if we don't have latency for all levels?
+		 */
+		latency = level == 0 ?
+			0 : skl_wm_latency(i915, level, NULL);
+
+		if (!skl_is_vblank_too_short(crtc_state, wm0_lines, latency))
+			return level;
+	}
+
+	return -EINVAL;
+}
+
+static int skl_wm_check_vblank(struct intel_crtc_state *crtc_state)
+{
+	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
+	struct drm_i915_private *i915 = to_i915(crtc->base.dev);
+	int level;
+
+	level = skl_max_wm_level_for_vblank(crtc_state);
+	if (level < 0)
+		return level;
+
+	/*
+	 * FIXME PSR needs to toggle LATENCY_REPORTING_REMOVED_PIPE_*
+	 * based on whether we're limited by the vblank duration.
+	 *
+	 * FIXME also related to skl+ w/a 1136 (also unimplemented as of
+	 * now) perhaps?
+	 */
+
+	for (level++; level <= ilk_wm_max_level(i915); level++) {
+		struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
+		enum plane_id plane_id;
+
+		for_each_plane_id_on_crtc(crtc, plane_id) {
+			struct skl_plane_wm *wm =
+				&crtc_state->wm.skl.optimal.planes[plane_id];
+
+			/*
+			 * FIXME just clear enable or flag the entire
+			 * thing as bad via min_ddb_alloc=U16_MAX?
+			 */
+			wm->wm[level].enable = false;
+			wm->uv_wm[level].enable = false;
+		}
+	}
+
+	return 0;
+}
+
 static int skl_build_pipe_wm(struct intel_atomic_state *state,
 			     struct intel_crtc *crtc)
 {
@@ -2224,7 +2318,7 @@ static int skl_build_pipe_wm(struct intel_atomic_state *state,
 
 	crtc_state->wm.skl.optimal = crtc_state->wm.skl.raw;
 
-	return 0;
+	return skl_wm_check_vblank(crtc_state);
 }
 
 static void skl_ddb_entry_write(struct drm_i915_private *i915,
-- 
2.38.2