[Intel-gfx] [PATCH] drm/i915: Query compressed bpp properly using correct DPCD and DP Spec info

[Stanislav Lisovskiy]

Currently we seem to be using wrong DPCD register for reading compressed bpps,
reading min/max input bpc instead of compressed bpp.
Fix that, so that we now apply min/max compressed bpp limitations we get
from DP Spec Table 2-157 DP v2.0 and/or correspondent DPCD register
DP_DSC_MAX_BITS_PER_PIXEL_LOW/HIGH.

This might also allow us to get rid of an ugly compressed bpp recalculation,
which we had to add to make some MST hubs usable.

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 76 ++++++++++++++-------
 1 file changed, 52 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index a88b852c437c..9479c7e0b269 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -174,6 +174,50 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
 	return 0;
 }
 
+static u16 dsc_max_sink_compressed_bppx16(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE],
+					  struct intel_crtc_state *pipe_config,
+					  int bpc)
+{
+	u16 max_bppx16 = dsc_dpcd[DP_DSC_MAX_BITS_PER_PIXEL_LOW - DP_DSC_SUPPORT] |
+			 (dsc_dpcd[DP_DSC_MAX_BITS_PER_PIXEL_HI - DP_DSC_SUPPORT] &
+			  DP_DSC_MAX_BITS_PER_PIXEL_HI_MASK << DP_DSC_MAX_BITS_PER_PIXEL_HI_SHIFT);
+
+	if (max_bppx16)
+		return max_bppx16;
+	/*
+	 * If support not given in DPCD 67h, 68h use the Maximum Allowed bit rate
+	 * values as given in spec Table 2-157 DP v2.0
+	 */
+	switch (pipe_config->output_format) {
+	case INTEL_OUTPUT_FORMAT_RGB:
+	case INTEL_OUTPUT_FORMAT_YCBCR444:
+		return bpc << 4;
+	case INTEL_OUTPUT_FORMAT_YCBCR420:
+		return (3 * (bpc / 2)) << 4;
+	default:
+		MISSING_CASE(pipe_config->output_format);
+		break;
+	}
+
+	return 0;
+}
+
+static u16 dsc_min_compressed_bppx16(struct intel_crtc_state *pipe_config)
+{
+	switch (pipe_config->output_format) {
+	case INTEL_OUTPUT_FORMAT_RGB:
+	case INTEL_OUTPUT_FORMAT_YCBCR444:
+		return 8 << 4;
+	case INTEL_OUTPUT_FORMAT_YCBCR420:
+		return 6 << 4;
+	default:
+		MISSING_CASE(pipe_config->output_format);
+		break;
+	}
+
+	return 0;
+}
+
 static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
 						struct intel_crtc_state *crtc_state,
 						struct drm_connector_state *conn_state,
@@ -191,8 +235,6 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
 	u8 dsc_bpc[3] = {0};
 	int min_bpp, max_bpp, sink_min_bpp, sink_max_bpp;
 	u8 dsc_max_bpc;
-	bool need_timeslot_recalc = false;
-	u32 last_compressed_bpp;
 
 	/* Max DSC Input BPC for ICL is 10 and for TGL+ is 12 */
 	if (DISPLAY_VER(i915) >= 12)
@@ -228,6 +270,14 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
 	if (max_bpp > sink_max_bpp)
 		max_bpp = sink_max_bpp;
 
+	/* Get Min/Max compressed bpp's for those Input Bpps we got for source/sink */
+	max_bpp = min(max_bpp, dsc_max_sink_compressed_bppx16(intel_dp->dsc_dpcd, crtc_state, max_bpp / 3) >> 4);
+	min_bpp = max(min_bpp, dsc_min_compressed_bppx16(crtc_state) >> 4);
+
+	/* Align compressed bpps according to our own constraints */
+	max_bpp = intel_dp_dsc_nearest_valid_bpp(i915, max_bpp, crtc_state->pipe_bpp);
+	min_bpp = intel_dp_dsc_nearest_valid_bpp(i915, min_bpp, crtc_state->pipe_bpp);
+
 	slots = intel_dp_mst_find_vcpi_slots_for_bpp(encoder, crtc_state, max_bpp,
 						     min_bpp, limits,
 						     conn_state, 2 * 3, true);
@@ -235,28 +285,6 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
 	if (slots < 0)
 		return slots;
 
-	last_compressed_bpp = crtc_state->dsc.compressed_bpp;
-
-	crtc_state->dsc.compressed_bpp = intel_dp_dsc_nearest_valid_bpp(i915,
-									last_compressed_bpp,
-									crtc_state->pipe_bpp);
-
-	if (crtc_state->dsc.compressed_bpp != last_compressed_bpp)
-		need_timeslot_recalc = true;
-
-	/*
-	 * Apparently some MST hubs dislike if vcpi slots are not matching precisely
-	 * the actual compressed bpp we use.
-	 */
-	if (need_timeslot_recalc) {
-		slots = intel_dp_mst_find_vcpi_slots_for_bpp(encoder, crtc_state,
-							     crtc_state->dsc.compressed_bpp,
-							     crtc_state->dsc.compressed_bpp,
-							     limits, conn_state, 2 * 3, true);
-		if (slots < 0)
-			return slots;
-	}
-
 	intel_link_compute_m_n(crtc_state->dsc.compressed_bpp,
 			       crtc_state->lane_count,
 			       adjusted_mode->crtc_clock,
-- 
2.37.3