drm/amd/display: Fix frames_to_insert math

[Why]
The math on deciding on how many
"frames to insert" sometimes sent us over the max refresh rate.
Also integer overflow can occur if we have high refresh rates.

[How]
Instead of clipping the  frame duration such that it doesn’t go below the min,
just remove a frame from the number of frames to insert. +
Use unsigned long long for intermediate calculations to prevent
integer overflow.

Signed-off-by: Bayan Zabihiyan <bayan.zabihiyan@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Bayan Zabihiyan

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

@@ -435,6 +435,12 @@ static void apply_below_the_range(struct core_freesync *core_freesync,
 		/* Either we've calculated the number of frames to insert,
 		 * or we need to insert min duration frames
 		 */
+		if (last_render_time_in_us / frames_to_insert <
+				in_out_vrr->min_duration_in_us){
+			frames_to_insert -= (frames_to_insert > 1) ?
+					1 : 0;
+		}
+
 		if (frames_to_insert > 0)
 			inserted_frame_duration_in_us = last_render_time_in_us /
 							frames_to_insert;
@@ -887,8 +893,8 @@ void mod_freesync_build_vrr_params(struct mod_freesync *mod_freesync,
 	struct core_freesync *core_freesync = NULL;
 	unsigned long long nominal_field_rate_in_uhz = 0;
 	unsigned int refresh_range = 0;
-	unsigned int min_refresh_in_uhz = 0;
-	unsigned int max_refresh_in_uhz = 0;
+	unsigned long long min_refresh_in_uhz = 0;
+	unsigned long long max_refresh_in_uhz = 0;
 
 	if (mod_freesync == NULL)
 		return;
@@ -915,7 +921,7 @@ void mod_freesync_build_vrr_params(struct mod_freesync *mod_freesync,
 		min_refresh_in_uhz = nominal_field_rate_in_uhz;
 
 	if (!vrr_settings_require_update(core_freesync,
-			in_config, min_refresh_in_uhz, max_refresh_in_uhz,
+			in_config, (unsigned int)min_refresh_in_uhz, (unsigned int)max_refresh_in_uhz,
 			in_out_vrr))
 		return;
 
@@ -931,15 +937,15 @@ void mod_freesync_build_vrr_params(struct mod_freesync *mod_freesync,
 		return;
 
 	} else {
-		in_out_vrr->min_refresh_in_uhz = min_refresh_in_uhz;
+		in_out_vrr->min_refresh_in_uhz = (unsigned int)min_refresh_in_uhz;
 		in_out_vrr->max_duration_in_us =
 				calc_duration_in_us_from_refresh_in_uhz(
-						min_refresh_in_uhz);
+						(unsigned int)min_refresh_in_uhz);
 
-		in_out_vrr->max_refresh_in_uhz = max_refresh_in_uhz;
+		in_out_vrr->max_refresh_in_uhz = (unsigned int)max_refresh_in_uhz;
 		in_out_vrr->min_duration_in_us =
 				calc_duration_in_us_from_refresh_in_uhz(
-						max_refresh_in_uhz);
+						(unsigned int)max_refresh_in_uhz);
 
 		refresh_range = in_out_vrr->max_refresh_in_uhz -
 				in_out_vrr->min_refresh_in_uhz;
@@ -950,17 +956,18 @@ void mod_freesync_build_vrr_params(struct mod_freesync *mod_freesync,
 	in_out_vrr->fixed.ramping_active = in_config->ramping;
 
 	in_out_vrr->btr.btr_enabled = in_config->btr;
+
 	if (in_out_vrr->max_refresh_in_uhz <
 			2 * in_out_vrr->min_refresh_in_uhz)
 		in_out_vrr->btr.btr_enabled = false;
+
 	in_out_vrr->btr.btr_active = false;
 	in_out_vrr->btr.inserted_duration_in_us = 0;
 	in_out_vrr->btr.frames_to_insert = 0;
 	in_out_vrr->btr.frame_counter = 0;
 	in_out_vrr->btr.mid_point_in_us =
-			in_out_vrr->min_duration_in_us +
-				(in_out_vrr->max_duration_in_us -
-				in_out_vrr->min_duration_in_us) / 2;
+				(in_out_vrr->min_duration_in_us +
+				 in_out_vrr->max_duration_in_us) / 2;
 
 	if (in_out_vrr->state == VRR_STATE_UNSUPPORTED) {
 		in_out_vrr->adjust.v_total_min = stream->timing.v_total;