[Intel-gfx] [PATCH] drm/i915: Fix FIFO underruns caused by missing cumulative bpp W/A

[Stanislav Lisovskiy]

We had some FIFO underruns appearing on platforms like ADL,
which could be fixed though by increasing CDCLK, however we were
lacking explanation for that - we were not calculating CDCLK,
also based on cumulative bpp W/A formula, mentioned in BSpec 64631.

With that patch no FIFO underruns appear anymore.

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
---
 drivers/gpu/drm/i915/display/intel_bw.c | 71 ++++++++++++++++++++++---
 drivers/gpu/drm/i915/display/intel_bw.h |  2 +
 2 files changed, 67 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_bw.c b/drivers/gpu/drm/i915/display/intel_bw.c
index 37bd7b17f3d0..3a2aeeffee7c 100644
--- a/drivers/gpu/drm/i915/display/intel_bw.c
+++ b/drivers/gpu/drm/i915/display/intel_bw.c
@@ -743,20 +743,51 @@ static void skl_plane_calc_dbuf_bw(struct intel_bw_state *bw_state,
 	}
 }
 
-static void skl_crtc_calc_dbuf_bw(struct intel_bw_state *bw_state,
+static int intel_plane_bw_bpp(const struct drm_format_info *info)
+{
+	/*
+	 * For the purposes of memory bandwidth calculations,
+	 * planar formats are treated as if both planes had the
+	 * same bpp (with no reduction for vertical
+	 * subsampling). I.e we take as usual the worst case
+	 * scenario.
+	 */
+	if (drm_format_info_is_yuv_semiplanar(info))
+		return 2 * max(info->cpp[0], info->cpp[1]);
+
+	return info->cpp[0];
+}
+
+static void skl_crtc_calc_dbuf_bw(struct intel_atomic_state *state,
+				  struct intel_bw_state *bw_state,
 				  const 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);
 	struct intel_dbuf_bw *crtc_bw = &bw_state->dbuf_bw[crtc->pipe];
-	enum plane_id plane_id;
+	struct intel_plane *plane;
 
 	memset(crtc_bw, 0, sizeof(*crtc_bw));
 
 	if (!crtc_state->hw.active)
 		return;
 
-	for_each_plane_id_on_crtc(crtc, plane_id) {
+	for_each_intel_plane_on_crtc(&i915->drm, crtc, plane) {
+		const struct drm_framebuffer *fb;
+		enum plane_id plane_id = plane->id;
+		unsigned int plane_bpp = 0;
+		struct intel_plane_state *plane_state =
+			intel_atomic_get_new_plane_state(state, plane);
+
+		if (plane_state) {
+			fb = plane_state->hw.fb;
+
+			if (plane_state->uapi.visible && fb)
+				plane_bpp = intel_plane_bw_bpp(fb->format);
+		}
+
+		crtc_bw->pipe_cumulative_bpp += plane_bpp;
+
 		/*
 		 * We assume cursors are small enough
 		 * to not cause bandwidth problems.
@@ -773,6 +804,10 @@ static void skl_crtc_calc_dbuf_bw(struct intel_bw_state *bw_state,
 					       &crtc_state->wm.skl.plane_ddb_y[plane_id],
 					       crtc_state->data_rate[plane_id]);
 	}
+
+	crtc_bw->bpp_cdclk = DIV_ROUND_UP_ULL(mul_u32_u32(crtc_state->pixel_rate,
+					      crtc_bw->pipe_cumulative_bpp * 512),
+					      10) / 1000;
 }
 
 /* "Maximum Data Buffer Bandwidth" */
@@ -782,11 +817,13 @@ intel_bw_dbuf_min_cdclk(struct drm_i915_private *i915,
 {
 	unsigned int total_max_bw = 0;
 	enum dbuf_slice slice;
+	enum pipe pipe;
+	unsigned int bpp_cdclk = 0;
+	unsigned int dbuf_bw_cdclk;
 
 	for_each_dbuf_slice(i915, slice) {
 		int num_active_planes = 0;
 		unsigned int max_bw = 0;
-		enum pipe pipe;
 
 		/*
 		 * The arbiter can only really guarantee an
@@ -803,7 +840,29 @@ intel_bw_dbuf_min_cdclk(struct drm_i915_private *i915,
 		total_max_bw = max(total_max_bw, max_bw);
 	}
 
-	return DIV_ROUND_UP(total_max_bw, 64);
+	for_each_pipe(i915, pipe) {
+		const struct intel_dbuf_bw *crtc_bw = &bw_state->dbuf_bw[pipe];
+		/*
+		 * From BSpec 64631:
+		 * Pipe cumulative bytes should be less or equal to
+		 * CDCLK / (pixel_rate * scaling_factors * 51.2) thus
+		 * CDCLK = pipe_cumulative_bpp * pixel_rate * scaling_factors * 51.2.
+		 * Considering that intel_plane_pixel_rate already returns adjusted pixel rate,
+		 * no scaling factors needed here.
+		 */
+		bpp_cdclk = max_t(unsigned int, crtc_bw->bpp_cdclk,
+						bpp_cdclk);
+	}
+
+	dbuf_bw_cdclk = DIV_ROUND_UP(total_max_bw, 64);
+
+	/*
+	 * So now we have two CDCLK estimations:
+	 * one is based on required DBuf BW and another is
+	 * based on pipe cumulative bpp W/A(BSpec 64631)
+	 * Traditionally take the more demanding into use(worst case)
+	 */
+	return max_t(unsigned int, dbuf_bw_cdclk, bpp_cdclk);
 }
 
 int intel_bw_min_cdclk(struct drm_i915_private *i915,
@@ -842,7 +901,7 @@ int intel_bw_calc_min_cdclk(struct intel_atomic_state *state,
 
 		old_bw_state = intel_atomic_get_old_bw_state(state);
 
-		skl_crtc_calc_dbuf_bw(new_bw_state, crtc_state);
+		skl_crtc_calc_dbuf_bw(state, new_bw_state, crtc_state);
 
 		new_bw_state->min_cdclk[crtc->pipe] =
 			intel_bw_crtc_min_cdclk(crtc_state);
diff --git a/drivers/gpu/drm/i915/display/intel_bw.h b/drivers/gpu/drm/i915/display/intel_bw.h
index cb7ee3a24a58..9e3a6ad03b19 100644
--- a/drivers/gpu/drm/i915/display/intel_bw.h
+++ b/drivers/gpu/drm/i915/display/intel_bw.h
@@ -19,6 +19,8 @@ struct intel_crtc_state;
 struct intel_dbuf_bw {
 	unsigned int max_bw[I915_MAX_DBUF_SLICES];
 	u8 active_planes[I915_MAX_DBUF_SLICES];
+	unsigned int pipe_cumulative_bpp;
+	unsigned int bpp_cdclk;
 };
 
 struct intel_bw_state {
-- 
2.24.1.485.gad05a3d8e5