drm/i915: Implement UHBR bandwidth check

According to spec, we should check if output_bpp * pixel_rate is less
than DDI clock * 72, if UHBR is used.

v2: - s/pipe_config/crtc_state/ (Jani Nikula)
    - Merged previous patch into that one, to remove empty function(Jani Nikula)

v3: - Make that constraint check to be DSC-related only
    - Limit this to only DISPLAY_VER <= 13

v4: - Move constraint check to the top(Vinod Govindapillai)

HSDES: 1406899791
BSPEC: 49259
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230324135125.6720-1-stanislav.lisovskiy@intel.com

drivers/gpu/drm/i915/display/intel_dp_mst.c

@@ -45,6 +45,27 @@
 #include "intel_hotplug.h"
 #include "skl_scaler.h"
 
+static int intel_dp_mst_check_constraints(struct drm_i915_private *i915, int bpp,
+					  const struct drm_display_mode *adjusted_mode,
+					  struct intel_crtc_state *crtc_state,
+					  bool dsc)
+{
+	if (intel_dp_is_uhbr(crtc_state) && DISPLAY_VER(i915) <= 13 && dsc) {
+		int output_bpp = bpp;
+		/* DisplayPort 2 128b/132b, bits per lane is always 32 */
+		int symbol_clock = crtc_state->port_clock / 32;
+
+		if (output_bpp * adjusted_mode->crtc_clock >=
+		    symbol_clock * 72) {
+			drm_dbg_kms(&i915->drm, "UHBR check failed(required bw %d available %d)\n",
+				    output_bpp * adjusted_mode->crtc_clock, symbol_clock * 72);
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
 static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
 						struct intel_crtc_state *crtc_state,
 						int max_bpp,
@@ -81,12 +102,16 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
 	}
 
 	for (bpp = max_bpp; bpp >= min_bpp; bpp -= step) {
+		drm_dbg_kms(&i915->drm, "Trying bpp %d\n", bpp);
+
+		ret = intel_dp_mst_check_constraints(i915, bpp, adjusted_mode, crtc_state, dsc);
+		if (ret)
+			continue;
+
 		crtc_state->pbn = drm_dp_calc_pbn_mode(adjusted_mode->crtc_clock,
 						       dsc ? bpp << 4 : bpp,
 						       dsc);
 
-		drm_dbg_kms(&i915->drm, "Trying bpp %d\n", bpp);
-
 		slots = drm_dp_atomic_find_time_slots(state, &intel_dp->mst_mgr,
 						      connector->port,
 						      crtc_state->pbn);
@@ -104,8 +129,8 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
 		}
 	}
 
-	/* Despite slots are non-zero, we still failed the atomic check */
-	if (ret && slots >= 0)
+	/* We failed to find a proper bpp/timeslots, return error */
+	if (ret)
 		slots = ret;
 
 	if (slots < 0) {