drm/amd/display: Block FPO According to Luminance Delta

[Description]
 - Block FPO if the max stretch refresh rate is low enough
   to cause a flicker by storing the maximum safe refresh
   decrease from nominal in stream.
 - Brought over various Freesync Luminance functions to dc. Use these
   new functions to block fpo if we will flicker.
 - Generalized increase/reduce dependent functions to reduce code clutter
   and allow for easier use.
 - Added a debug option to enable the feature. Disabled by default.
Co-authored-by: Ethan Bitnun <etbitnun@amd.com>
Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Ethan Bitnun <etbitnun@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/core/dc_stream.c

@@ -35,6 +35,8 @@
 #include "dc_stream_priv.h"
 
 #define DC_LOGGER dc->ctx->logger
+#define MIN(X, Y) ((X) < (Y) ? (X) : (Y))
+#define MAX(x, y) ((x > y) ? x : y)
 
 /*******************************************************************************
  * Private functions
@@ -781,3 +783,229 @@ void dc_stream_log(const struct dc *dc, const struct dc_stream_state *stream)
 	}
 }
 
+/*
+ * Finds the greatest index in refresh_rate_hz that contains a value <= refresh
+ */
+static int dc_stream_get_nearest_smallest_index(struct dc_stream_state *stream, int refresh)
+{
+	for (int i = 0; i < (LUMINANCE_DATA_TABLE_SIZE - 1); ++i) {
+		if ((stream->lumin_data.refresh_rate_hz[i] <= refresh) && (refresh < stream->lumin_data.refresh_rate_hz[i + 1])) {
+			return i;
+		}
+	}
+	return 9;
+}
+
+/*
+ * Finds a corresponding brightness for a given refresh rate between 2 given indices, where index1 < index2
+ */
+static int dc_stream_get_brightness_millinits_linear_interpolation (struct dc_stream_state *stream,
+								     int index1,
+								     int index2,
+								     int refresh_hz)
+{
+	int slope = 0;
+	if (stream->lumin_data.refresh_rate_hz[index2] != stream->lumin_data.refresh_rate_hz[index1]) {
+		slope = (stream->lumin_data.luminance_millinits[index2] - stream->lumin_data.luminance_millinits[index1]) /
+			    (stream->lumin_data.refresh_rate_hz[index2] - stream->lumin_data.refresh_rate_hz[index1]);
+	}
+
+	int y_intercept = stream->lumin_data.luminance_millinits[index2] - slope * stream->lumin_data.refresh_rate_hz[index2];
+
+	return (y_intercept + refresh_hz * slope);
+}
+
+/*
+ * Finds a corresponding refresh rate for a given brightness between 2 given indices, where index1 < index2
+ */
+static int dc_stream_get_refresh_hz_linear_interpolation (struct dc_stream_state *stream,
+							   int index1,
+							   int index2,
+							   int brightness_millinits)
+{
+	int slope = 1;
+	if (stream->lumin_data.refresh_rate_hz[index2] != stream->lumin_data.refresh_rate_hz[index1]) {
+		slope = (stream->lumin_data.luminance_millinits[index2] - stream->lumin_data.luminance_millinits[index1]) /
+				(stream->lumin_data.refresh_rate_hz[index2] - stream->lumin_data.refresh_rate_hz[index1]);
+	}
+
+	int y_intercept = stream->lumin_data.luminance_millinits[index2] - slope * stream->lumin_data.refresh_rate_hz[index2];
+
+	return ((brightness_millinits - y_intercept) / slope);
+}
+
+/*
+ * Finds the current brightness in millinits given a refresh rate
+ */
+static int dc_stream_get_brightness_millinits_from_refresh (struct dc_stream_state *stream, int refresh_hz)
+{
+	int nearest_smallest_index = dc_stream_get_nearest_smallest_index(stream, refresh_hz);
+	int nearest_smallest_value = stream->lumin_data.refresh_rate_hz[nearest_smallest_index];
+
+	if (nearest_smallest_value == refresh_hz)
+		return stream->lumin_data.luminance_millinits[nearest_smallest_index];
+
+	if (nearest_smallest_index >= 9)
+		return dc_stream_get_brightness_millinits_linear_interpolation(stream, nearest_smallest_index - 1, nearest_smallest_index, refresh_hz);
+
+	if (nearest_smallest_value == stream->lumin_data.refresh_rate_hz[nearest_smallest_index + 1])
+		return stream->lumin_data.luminance_millinits[nearest_smallest_index];
+
+	return dc_stream_get_brightness_millinits_linear_interpolation(stream, nearest_smallest_index, nearest_smallest_index + 1, refresh_hz);
+}
+
+/*
+ * Finds the lowest refresh rate that can be achieved
+ * from starting_refresh_hz while staying within flicker criteria
+ */
+static int dc_stream_calculate_flickerless_refresh_rate(struct dc_stream_state *stream,
+							 int current_brightness,
+							 int starting_refresh_hz,
+							 bool is_gaming,
+							 bool search_for_max_increase)
+{
+	int nearest_smallest_index = dc_stream_get_nearest_smallest_index(stream, starting_refresh_hz);
+
+	int flicker_criteria_millinits = is_gaming ?
+					 stream->lumin_data.flicker_criteria_milli_nits_GAMING :
+					 stream->lumin_data.flicker_criteria_milli_nits_STATIC;
+
+	int safe_upper_bound = current_brightness + flicker_criteria_millinits;
+	int safe_lower_bound = current_brightness - flicker_criteria_millinits;
+	int lumin_millinits_temp = 0;
+
+	int offset = -1;
+	if (search_for_max_increase) {
+		offset = 1;
+	}
+
+	/*
+	 * Increments up or down by 1 depending on search_for_max_increase
+	 */
+	for (int i = nearest_smallest_index; (i > 0 && !search_for_max_increase) || (i < (LUMINANCE_DATA_TABLE_SIZE - 1) && search_for_max_increase); i += offset) {
+
+		lumin_millinits_temp = stream->lumin_data.luminance_millinits[i + offset];
+
+		if ((lumin_millinits_temp >= safe_upper_bound) || (lumin_millinits_temp <= safe_lower_bound)) {
+
+			if (stream->lumin_data.refresh_rate_hz[i + offset] == stream->lumin_data.refresh_rate_hz[i])
+				return stream->lumin_data.refresh_rate_hz[i];
+
+			int target_brightness = (stream->lumin_data.luminance_millinits[i + offset] >= (current_brightness + flicker_criteria_millinits)) ?
+											current_brightness + flicker_criteria_millinits :
+											current_brightness - flicker_criteria_millinits;
+
+			int refresh = 0;
+
+			/*
+			 * Need the second input to be < third input for dc_stream_get_refresh_hz_linear_interpolation
+			 */
+			if (search_for_max_increase)
+				refresh = dc_stream_get_refresh_hz_linear_interpolation(stream, i, i + offset, target_brightness);
+			else
+				refresh = dc_stream_get_refresh_hz_linear_interpolation(stream, i + offset, i, target_brightness);
+
+			if (refresh == stream->lumin_data.refresh_rate_hz[i + offset])
+				return stream->lumin_data.refresh_rate_hz[i + offset];
+
+			return refresh;
+		}
+	}
+
+	if (search_for_max_increase)
+		return stream->lumin_data.refresh_rate_hz[LUMINANCE_DATA_TABLE_SIZE - 1];
+	else
+		return stream->lumin_data.refresh_rate_hz[0];
+}
+
+/*
+ * Gets the max delta luminance within a specified refresh range
+ */
+static int dc_stream_get_max_delta_lumin_millinits(struct dc_stream_state *stream, int hz1, int hz2, bool isGaming)
+{
+	int lower_refresh_brightness = dc_stream_get_brightness_millinits_from_refresh (stream, hz1);
+	int higher_refresh_brightness = dc_stream_get_brightness_millinits_from_refresh (stream, hz2);
+
+	int min = lower_refresh_brightness;
+	int max = higher_refresh_brightness;
+
+	/*
+	 * Static screen, therefore no need to scan through array
+	 */
+	if (!isGaming) {
+		if (lower_refresh_brightness >= higher_refresh_brightness) {
+			return lower_refresh_brightness - higher_refresh_brightness;
+		}
+		return higher_refresh_brightness - lower_refresh_brightness;
+	}
+
+	min = MIN(lower_refresh_brightness, higher_refresh_brightness);
+	max = MAX(lower_refresh_brightness, higher_refresh_brightness);
+
+	int nearest_smallest_index = dc_stream_get_nearest_smallest_index(stream, hz1);
+
+	for (; nearest_smallest_index < (LUMINANCE_DATA_TABLE_SIZE - 1) &&
+			stream->lumin_data.refresh_rate_hz[nearest_smallest_index + 1] <= hz2 ; nearest_smallest_index++) {
+		min = MIN(min, stream->lumin_data.luminance_millinits[nearest_smallest_index + 1]);
+		max = MAX(max, stream->lumin_data.luminance_millinits[nearest_smallest_index + 1]);
+	}
+
+	return (max - min);
+}
+
+/*
+ * Finds the highest refresh rate that can be achieved
+ * from starting_refresh_hz while staying within flicker criteria
+ */
+int dc_stream_calculate_max_flickerless_refresh_rate(struct dc_stream_state *stream, int starting_refresh_hz, bool is_gaming)
+{
+	if (!stream->lumin_data.is_valid)
+		return 0;
+
+	int current_brightness = dc_stream_get_brightness_millinits_from_refresh(stream, starting_refresh_hz);
+
+	return dc_stream_calculate_flickerless_refresh_rate(stream,
+							    current_brightness,
+							    starting_refresh_hz,
+							    is_gaming,
+							    true);
+}
+
+/*
+ * Finds the lowest refresh rate that can be achieved
+ * from starting_refresh_hz while staying within flicker criteria
+ */
+int dc_stream_calculate_min_flickerless_refresh_rate(struct dc_stream_state *stream, int starting_refresh_hz, bool is_gaming)
+{
+	if (!stream->lumin_data.is_valid)
+			return 0;
+
+	int current_brightness = dc_stream_get_brightness_millinits_from_refresh(stream, starting_refresh_hz);
+
+	return dc_stream_calculate_flickerless_refresh_rate(stream,
+							    current_brightness,
+							    starting_refresh_hz,
+							    is_gaming,
+							    false);
+}
+
+/*
+ * Determines if there will be a flicker when moving between 2 refresh rates
+ */
+bool dc_stream_is_refresh_rate_range_flickerless(struct dc_stream_state *stream, int hz1, int hz2, bool is_gaming)
+{
+
+	/*
+	 * Assume that we wont flicker if there is invalid data
+	 */
+	if (!stream->lumin_data.is_valid)
+		return false;
+
+	int dl = dc_stream_get_max_delta_lumin_millinits(stream, hz1, hz2, is_gaming);
+
+	int flicker_criteria_millinits = (is_gaming) ?
+					  stream->lumin_data.flicker_criteria_milli_nits_GAMING :
+					  stream->lumin_data.flicker_criteria_milli_nits_STATIC;
+
+	return (dl <= flicker_criteria_millinits);
+}

drivers/gpu/drm/amd/display/dc/dc.h

@@ -456,6 +456,7 @@ struct dc_config {
 	bool allow_0_dtb_clk;
 	bool use_assr_psp_message;
 	bool support_edp0_on_dp1;
+	unsigned int enable_fpo_flicker_detection;
 };
 
 enum visual_confirm {

drivers/gpu/drm/amd/display/dc/dc_stream.h

@@ -160,6 +160,18 @@ struct dc_stream_debug_options {
 	char force_odm_combine_segments;
 };
 
+#define LUMINANCE_DATA_TABLE_SIZE 10
+
+struct luminance_data {
+	bool is_valid;
+	int refresh_rate_hz[LUMINANCE_DATA_TABLE_SIZE];
+	int luminance_millinits[LUMINANCE_DATA_TABLE_SIZE];
+	int flicker_criteria_milli_nits_GAMING;
+	int flicker_criteria_milli_nits_STATIC;
+	int nominal_refresh_rate;
+	int dm_max_decrease_from_nominal;
+};
+
 struct dc_stream_state {
 	// sink is deprecated, new code should not reference
 	// this pointer
@@ -286,6 +298,8 @@ struct dc_stream_state {
 	bool vblank_synchronized;
 	bool fpo_in_use;
 	bool is_phantom;
+
+	struct luminance_data lumin_data;
 };
 
 #define ABM_LEVEL_IMMEDIATE_DISABLE 255

drivers/gpu/drm/amd/display/dc/dc_stream_priv.h

@@ -34,4 +34,28 @@ void dc_stream_destruct(struct dc_stream_state *stream);
 
 void dc_stream_assign_stream_id(struct dc_stream_state *stream);
 
+/*
+ * Finds the highest refresh rate that can be achieved
+ * from starting_freq while staying within flicker criteria
+ */
+int dc_stream_calculate_max_flickerless_refresh_rate(struct dc_stream_state *stream,
+						      int starting_refresh_hz,
+						      bool is_gaming);
+
+/*
+ * Finds the lowest refresh rate that can be achieved
+ * from starting_freq while staying within flicker criteria
+ */
+int dc_stream_calculate_min_flickerless_refresh_rate(struct dc_stream_state *stream,
+						      int starting_refresh_hz,
+						      bool is_gaming);
+
+/*
+ * Determines if there will be a flicker when moving between 2 refresh rates
+ */
+bool dc_stream_is_refresh_rate_range_flickerless(struct dc_stream_state *stream,
+						  int hz1,
+						  int hz2,
+						  bool is_gaming);
+
 #endif // _DC_STREAM_PRIV_H_

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

@@ -29,6 +29,7 @@
 #include "dml/dcn32/display_mode_vba_util_32.h"
 #include "dml/dcn32/dcn32_fpu.h"
 #include "dc_state_priv.h"
+#include "dc_stream_priv.h"
 
 static bool is_dual_plane(enum surface_pixel_format format)
 {
@@ -459,7 +460,7 @@ static int get_frame_rate_at_max_stretch_100hz(
 }
 
 static bool is_refresh_rate_support_mclk_switch_using_fw_based_vblank_stretch(
-		struct dc_stream_state *fpo_candidate_stream, uint32_t fpo_vactive_margin_us)
+		struct dc_stream_state *fpo_candidate_stream, uint32_t fpo_vactive_margin_us, int current_refresh_rate)
 {
 	int refresh_rate_max_stretch_100hz;
 	int min_refresh_100hz;
@@ -473,6 +474,10 @@ static bool is_refresh_rate_support_mclk_switch_using_fw_based_vblank_stretch(
 	if (refresh_rate_max_stretch_100hz < min_refresh_100hz)
 		return false;
 
+	if (fpo_candidate_stream->ctx->dc->config.enable_fpo_flicker_detection > 0 &&
+			!dc_stream_is_refresh_rate_range_flickerless(fpo_candidate_stream, (refresh_rate_max_stretch_100hz / 100), current_refresh_rate, false))
+		return false;
+
 	return true;
 }
 
@@ -569,7 +574,7 @@ struct dc_stream_state *dcn32_can_support_mclk_switch_using_fw_based_vblank_stre
 		return NULL;
 
 	fpo_vactive_margin_us = is_fpo_vactive ? dc->debug.fpo_vactive_margin_us : 0; // For now hardcode the FPO + Vactive stretch margin to be 2000us
-	if (!is_refresh_rate_support_mclk_switch_using_fw_based_vblank_stretch(fpo_candidate_stream, fpo_vactive_margin_us))
+	if (!is_refresh_rate_support_mclk_switch_using_fw_based_vblank_stretch(fpo_candidate_stream, fpo_vactive_margin_us, refresh_rate))
 		return NULL;
 
 	if (!fpo_candidate_stream->allow_freesync)