drm/amd/display: reallocate DET for dual displays with high pixel rate ratio

[Why]
For dual displays where pixel rate is much higher on one display,
we may get underflow when DET is evenly allocated.

[How]
Allocate less DET segments for the lower pixel rate display and
more DET segments for the higher pixel rate display
Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Samson Tam <Samson.Tam@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn32/dcn32_resource_helpers.c

@@ -257,6 +257,8 @@ bool dcn32_is_psr_capable(struct pipe_ctx *pipe)
 	return psr_capable;
 }
 
+#define DCN3_2_NEW_DET_OVERRIDE_MIN_MULTIPLIER 7
+
 /**
  * *******************************************************************************************
  * dcn32_determine_det_override: Determine DET allocation for each pipe
@@ -268,7 +270,6 @@ bool dcn32_is_psr_capable(struct pipe_ctx *pipe)
  * If there is a plane that's driven by more than 1 pipe (i.e. pipe split), then the
  * number of DET for that given plane will be split among the pipes driving that plane.
  *
- *
  * High level algorithm:
  * 1. Split total DET among number of streams
  * 2. For each stream, split DET among the planes
@@ -276,6 +277,18 @@ bool dcn32_is_psr_capable(struct pipe_ctx *pipe)
  *    among those pipes.
  * 4. Assign the DET override to the DML pipes.
  *
+ * Special cases:
+ *
+ * For two displays that have a large difference in pixel rate, we may experience
+ *  underflow on the larger display when we divide the DET equally. For this, we
+ *  will implement a modified algorithm to assign more DET to larger display.
+ *
+ * 1. Calculate difference in pixel rates ( multiplier ) between two displays
+ * 2. If the multiplier exceeds DCN3_2_NEW_DET_OVERRIDE_MIN_MULTIPLIER, then
+ *    implement the modified DET override algorithm.
+ * 3. Assign smaller DET size for lower pixel display and higher DET size for
+ *    higher pixel display
+ *
  * @param [in]: dc: Current DC state
  * @param [in]: context: New DC state to be programmed
  * @param [in]: pipes: Array of DML pipes
@@ -295,18 +308,46 @@ void dcn32_determine_det_override(struct dc *dc,
 	struct dc_plane_state *current_plane = NULL;
 	uint8_t stream_count = 0;
 
+	int phy_pix_clk_mult, lower_mode_stream_index;
+	int phy_pix_clk[MAX_PIPES] = {0};
+	bool use_new_det_override_algorithm = false;
+
 	for (i = 0; i < context->stream_count; i++) {
 		/* Don't count SubVP streams for DET allocation */
 		if (context->streams[i]->mall_stream_config.type != SUBVP_PHANTOM) {
+			phy_pix_clk[i] = context->streams[i]->phy_pix_clk;
 			stream_count++;
 		}
 	}
 
+	/* Check for special case with two displays, one with much higher pixel rate */
+	if (stream_count == 2) {
+		ASSERT(!phy_pix_clk[0] || !phy_pix_clk[1]);
+		if (phy_pix_clk[0] < phy_pix_clk[1]) {
+			lower_mode_stream_index = 0;
+			phy_pix_clk_mult = phy_pix_clk[1] / phy_pix_clk[0];
+		} else {
+			lower_mode_stream_index = 1;
+			phy_pix_clk_mult = phy_pix_clk[0] / phy_pix_clk[1];
+		}
+
+		if (phy_pix_clk_mult >= DCN3_2_NEW_DET_OVERRIDE_MIN_MULTIPLIER)
+			use_new_det_override_algorithm = true;
+	}
+
 	if (stream_count > 0) {
 		stream_segments = 18 / stream_count;
 		for (i = 0; i < context->stream_count; i++) {
 			if (context->streams[i]->mall_stream_config.type == SUBVP_PHANTOM)
 				continue;
+
+			if (use_new_det_override_algorithm) {
+				if (i == lower_mode_stream_index)
+					stream_segments = 4;
+				else
+					stream_segments = 14;
+			}
+
 			if (context->stream_status[i].plane_count > 0)
 				plane_segments = stream_segments / context->stream_status[i].plane_count;
 			else