drm/amd/display: Add flip interval workaround

[WHY]
Some games experience low FPS issues when FreeSync is on and VSync is
toggled to half refresh rate.

[HOW]
First create a function to determine workaround conditions, which is
when we detect 2 or more VSync interrupts between flips and a very short
VSync to flip interval. We do the workaround during VSync interrupts and
set the v_total_max and min to nominal. We also cleanup after we exit
the game.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Angus Wang <Angus.Wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/modules/freesync/freesync.c

@@ -29,6 +29,7 @@
 #include "dc.h"
 #include "mod_freesync.h"
 #include "core_types.h"
+#include "dm_services.h"
 
 #define MOD_FREESYNC_MAX_CONCURRENT_STREAMS  32
 
@@ -46,6 +47,10 @@
 /* Number of consecutive frames to check before entering/exiting fixed refresh */
 #define FIXED_REFRESH_ENTER_FRAME_COUNT 5
 #define FIXED_REFRESH_EXIT_FRAME_COUNT 10
+/* Flip interval workaround constants */
+#define VSYNCS_BETWEEN_FLIP_THRESHOLD 2
+#define FREESYNC_CONSEC_FLIP_AFTER_VSYNC 5
+#define FREESYNC_VSYNC_TO_FLIP_DELTA_IN_US 500
 
 struct core_freesync {
 	struct mod_freesync public;
@@ -466,6 +471,41 @@ static void apply_fixed_refresh(struct core_freesync *core_freesync,
 	}
 }
 
+static void determine_flip_interval_workaround_req(struct mod_vrr_params *in_vrr,
+		unsigned int curr_time_stamp_in_us)
+{
+	in_vrr->flip_interval.vsync_to_flip_in_us = curr_time_stamp_in_us -
+			in_vrr->flip_interval.v_update_timestamp_in_us;
+
+	/* Determine conditions for stopping workaround */
+	if (in_vrr->flip_interval.flip_interval_workaround_active &&
+			in_vrr->flip_interval.vsyncs_between_flip < VSYNCS_BETWEEN_FLIP_THRESHOLD &&
+			in_vrr->flip_interval.vsync_to_flip_in_us > FREESYNC_VSYNC_TO_FLIP_DELTA_IN_US) {
+		in_vrr->flip_interval.flip_interval_detect_counter = 0;
+		in_vrr->flip_interval.program_flip_interval_workaround = true;
+		in_vrr->flip_interval.flip_interval_workaround_active = false;
+	} else {
+		/* Determine conditions for starting workaround */
+		if (in_vrr->flip_interval.vsyncs_between_flip >= VSYNCS_BETWEEN_FLIP_THRESHOLD &&
+				in_vrr->flip_interval.vsync_to_flip_in_us < FREESYNC_VSYNC_TO_FLIP_DELTA_IN_US) {
+			/* Increase flip interval counter we have 2 vsyncs between flips and
+			 * vsync to flip interval is less than 500us
+			 */
+			in_vrr->flip_interval.flip_interval_detect_counter++;
+			if (in_vrr->flip_interval.flip_interval_detect_counter > FREESYNC_CONSEC_FLIP_AFTER_VSYNC) {
+				/* Start workaround if we detect 5 consecutive instances of the above case */
+				in_vrr->flip_interval.program_flip_interval_workaround = true;
+				in_vrr->flip_interval.flip_interval_workaround_active = true;
+			}
+		} else {
+			/* Reset the flip interval counter if we condition is no longer met */
+			in_vrr->flip_interval.flip_interval_detect_counter = 0;
+		}
+	}
+
+	in_vrr->flip_interval.vsyncs_between_flip = 0;
+}
+
 static bool vrr_settings_require_update(struct core_freesync *core_freesync,
 		struct mod_freesync_config *in_config,
 		unsigned int min_refresh_in_uhz,
@@ -1179,6 +1219,9 @@ void mod_freesync_handle_preflip(struct mod_freesync *mod_freesync,
 				in_out_vrr);
 		}
 
+		determine_flip_interval_workaround_req(in_out_vrr,
+				curr_time_stamp_in_us);
+
 	}
 }
 
@@ -1187,6 +1230,7 @@ void mod_freesync_handle_v_update(struct mod_freesync *mod_freesync,
 		struct mod_vrr_params *in_out_vrr)
 {
 	struct core_freesync *core_freesync = NULL;
+	unsigned int cur_timestamp_in_us;
 
 	if ((mod_freesync == NULL) || (stream == NULL) || (in_out_vrr == NULL))
 		return;
@@ -1196,6 +1240,34 @@ void mod_freesync_handle_v_update(struct mod_freesync *mod_freesync,
 	if (in_out_vrr->supported == false)
 		return;
 
+	cur_timestamp_in_us = dm_get_timestamp(core_freesync->dc->ctx)/10;
+
+	in_out_vrr->flip_interval.vsyncs_between_flip++;
+	in_out_vrr->flip_interval.v_update_timestamp_in_us = cur_timestamp_in_us;
+
+	if (in_out_vrr->state == VRR_STATE_ACTIVE_VARIABLE &&
+			(in_out_vrr->flip_interval.flip_interval_workaround_active ||
+			(!in_out_vrr->flip_interval.flip_interval_workaround_active &&
+			in_out_vrr->flip_interval.program_flip_interval_workaround))) {
+		// set freesync vmin vmax to nominal for workaround
+		in_out_vrr->adjust.v_total_min =
+			mod_freesync_calc_v_total_from_refresh(
+			stream, in_out_vrr->max_refresh_in_uhz);
+		in_out_vrr->adjust.v_total_max =
+				in_out_vrr->adjust.v_total_min;
+		in_out_vrr->flip_interval.program_flip_interval_workaround = false;
+		in_out_vrr->flip_interval.do_flip_interval_workaround_cleanup = true;
+		return;
+	}
+
+	if (in_out_vrr->state != VRR_STATE_ACTIVE_VARIABLE &&
+			in_out_vrr->flip_interval.do_flip_interval_workaround_cleanup) {
+		in_out_vrr->flip_interval.do_flip_interval_workaround_cleanup = false;
+		in_out_vrr->flip_interval.flip_interval_detect_counter = 0;
+		in_out_vrr->flip_interval.vsyncs_between_flip = 0;
+		in_out_vrr->flip_interval.vsync_to_flip_in_us = 0;
+	}
+
 	/* Below the Range Logic */
 
 	/* Only execute if in fullscreen mode */

drivers/gpu/drm/amd/display/modules/inc/mod_freesync.h

@@ -105,6 +105,16 @@ struct mod_vrr_params_fixed_refresh {
 	uint32_t frame_counter;
 };
 
+struct mod_vrr_params_flip_interval {
+	bool flip_interval_workaround_active;
+	bool program_flip_interval_workaround;
+	bool do_flip_interval_workaround_cleanup;
+	uint32_t flip_interval_detect_counter;
+	uint32_t vsyncs_between_flip;
+	uint32_t vsync_to_flip_in_us;
+	uint32_t v_update_timestamp_in_us;
+};
+
 struct mod_vrr_params {
 	bool supported;
 	bool send_info_frame;
@@ -121,6 +131,8 @@ struct mod_vrr_params {
 	struct mod_vrr_params_fixed_refresh fixed;
 
 	struct mod_vrr_params_btr btr;
+
+	struct mod_vrr_params_flip_interval flip_interval;
 };
 
 struct mod_freesync *mod_freesync_create(struct dc *dc);